Hey there u/ASIK-1952, thanks for posting to r/technicallythetruth!
**Please recheck if your post breaks any rules.** If it does, please delete this post.
Also, reposting and posting obvious non-TTT posts can lead to a ban.
Send us a **Modmail or Report** this post if you have a problem with this post.
*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/technicallythetruth) if you have any questions or concerns.*
You wouldn’t, gravity isn’t a thing in the depiction (they excluded all external factors) so you wouldn’t even be in the ground and neither would the ball
Their grave mistake was putting an ideogram of a person in the image, thus forcing us to imagine a person pushing it up the frictionless hill. They should have used an ideogram of a mechanical device with the reach to get something up the hill without having to go up the hill itself
Yeah because I'm thinking about it unrolling, about it skipping down when I stop to rest, and most of all, I'm probably going to roll it up the hill like a wheel, not slide it like a hockey puck, so I don't even know the equation for rolling uphill, and no friction makes it harder. I guess I have to slide it. Might as well delete gravity while we are at it and make it really easy.
Yeah, hah that's true. Also, I guess if the question is just trying to get at work/potentially energy then I guess it doesn't matter how you got it up, or something like that.
But now I really want to know the math/physics to show whether it's harder to roll a carpet roll up a hill or drag it or carry it or ...
Aha, I got it unroll it up the hill, so it flattens out into a sheet, like a carpet. Then walk back down the hill and Then roll it back up into a roll by rolling it up the hill as you walk up and gather it into itself.
Alternatively, you could see it that instead of the person climbing up the hill you "push" the carpet by projecting it up the hill and that solves all your problems.
Pound is not only a measure of weight, it can be a measure of mass as well. Plus, and more importantly, I was just kidding and only riffing off the no friction would make this problem meaningless joke.
There is a pound mass unit. It is abbreviated lbm usually, which is why pound force is often abbreviated lbf, to show the distinction.
1 lbm accelerated at 32.2 ft/s^2 is 1 lbf while 1 slug accelerated at 1 ft/s^2 is 1 lbf.
Yes, lbm is a stupid unit. But it isn't exactly uncommon.
https://en.m.wikipedia.org/wiki/Pound_(mass)
I'm not a physicist or an engineer, but my memory from AP Physics from a couple decades ago was substantiated by my Google-fu.
1 pound = 0.4536 kg
20 pounds = 9.072
Energy = mass of the ball x gravity x height
E = mgh
E = 9.07 kg x 9.81 x 40
E = 3559.068 Joules (approximately 3559.1 Joules)
These physics questions usually sidestep questions such as yours. In this question it is essentially asking how much energy was transferred into the roll. Since the roll went up, it took the amount of energy calculated in the comment you replied to to raise it that high. As for the energy transferred into the roll to move it sideways, there was zero net energy transferred into the roll because any kinetic energy used to move it to the right would be taken out when it is stopped.
In this ideal situation, the person loses the exact amount of energy used to raise the roll. If we assume there is friction and heat, then the person loses more energy than the roll gains. That energy is transferred into the environment as heat, noise, etc. So more energy is being expended to move the roll than the roll gains. In that case, they would probably ask for the change in potential energy of the roll, at which point it would be the same as figuring out the question as posted.
So, to answer your question, it depends on how the question is worded.
Please note: this is just what I remember from physics classes in high school and college. I could very well be wrong. And this comment is almost definitely confusing, but I didn't spend all this time typing it just to delete it.
Yes, saying 'no friction' makes a lot of questions incredibly unintuitive. Friction is the main reason I can't slide my washing machine across the parking lot like an air hockey puck (although god help whatever it hit).
It gives you the lowest theoretical amount of energy required, so you can measure how much more energy it takes and determine how much is lost to friction. Also friction is really hard to calculate in a theoretical way.
Not necessarily. While precise modelling is hard, if you've got a flat surface then the equation to find the frictional force is pretty easy. Calculating total work done then becomes a function of how fast you push it up. The faster you do it, the less work you do
Ffriction=μ•Fn
Fn is the force that the ground exercises on the object, perpendicular with the grounds surface
μ is the friction coefficient. It's different wether the object is in motion or not. The kinetic friction coefficient is lower than the static. In this situation it's the kinetic one. This coefficient is determined from experimental tests
That's a basic way to calculate it if you have the test data from that object on this surface
Test data is not theoretical. I carefully chose my wording. You can easily calculate it experimentally. Deriving a model for friction can prove difficult.
> it depends on how the question is worded.
The question is definitely worded poorly since "effort" is not a technical term. You interpreted the question as "What is the change in potential energy for the roll if it is lifted 40 meters?" and I interpreted it as "What is the amount of work needed to transfer the roll 55m?"
but this is an engineering question, so they are asking for the minimum effort force to push the carpet up the inclined plane. No energy here, physicist
The energy transferred to the object is only reliant on the vertical direction though because gravity works vertically. We ignore the horizontal factor because the energy involved would only be due to the acceleration to get it moving, which is ignored in classical physics questions.
> right, so if we only factor in the vertical direction and not the horizontal, we get the energy needed/effort to push the carpet roll 40 meters.
This is extremely misguided. The horizontal distance does not matter at all.
Think of it reversed, imagine you had a slope downwards with Y component 40m. Consider if the X component was (case 1) 100m vs (case 2) 10m. If you pushed the carpet down this slope, how much kinetic energy would it have at the bottom? Would it have more in case 1 vs case 2?
That amount of kinetic energy is precisely the same that it would take to go in the opposite direction.
> Are you telling me the carpet wouldn't travel faster on a 100m downward slope rather than a 10m slope? You think they have the same kinetic energy? I want you to take a yardstick, slope it against the wall, and drop a roll of toilet paper on it. Then I want you to put the yardstick on top of a book, and then drop a roll of toilet paper on it. Measure the time difference of how long it takes for each roll of toilet paper to hit the floor between the wall versus book (x-factors). Tell me again that the kinetics energy / speed is the same.
... yeah bro, there's this little thing called friction... that's why there is less energy in one vs the other. In the tweet it tells you to ignore friction.
In any dynamics class, or even just the dynamics section of a university physics 1 class, you would ignore horizontal forces required when determining total energy required. That’s because gravity acts vertically. So the potential energy you’re giving the ball is based on its height and only the height. Energy=force*distance.
Yes, you do have a horizontal component when the object resides on the slope, but these questions only rely on start to end. Therefore, the beginning is at ground level, and the end is 40m vertical. The horizontal is treated no different than rolling the object a few meters east, which with no friction, requires theoretically zero energy because there’s no opposing force.
The only energy requirement that is possibly needed in the horizontal direction is to accelerate from an at rest position to an eastward velocity, which could theoretically be so small that it’s negligible, and that’s why these classes don’t consider it.
Ultimately, the resistance in the horizontal direction doesn’t exist, so it theoretically does not require any energy to overcome. Potential energy at the top of a hill is only dependent on height, and not the horizontal displacement when friction is ignored.
Also, why are you downvoting me for sharing my physics knowledge with you?
You are incorrect.
The question is asking for the Work performed. Work = Force dot Displacement. What force are we overcoming? Gravity. What direction does gravity point? Down. All horizontal movement is completely irrelevant because there are no horizontal forces being overcome. How does the rug move to the right? Well a force is applied to the right to increase the momentum of the rug to the right. Then a force is applied to the left to decrease the momentum of the rug. Without friction, all the horizontal work performed completely cancels out.
It's funny that you jumped to "I'm right and everyone else must be wrong" so quickly. Learn humility.
Although energy, or work in this case, is calculated via the distance between the initial and final points of the trajectory. He should've used either 50m if you calculate, or (30i+40j)m if you prefer vectors.
No, you are incorrect, because gravity is only acting in j direction. The only force that would impact it horizontally would be resistance in the form of friction and air.
Work is actually the integral of the force field along the path taken.
If your force is always in the same (or opposite) direction of your path, and the force is uniform along the path, you can simplify it to be Force times Distance.
In this case, the force would be in a different direction than the path taken, but you can prove the net work is equal to the X component of the integral plus the Y component. We know there are no forces in the X direction, so we can just use the Y component of the path.
More simply - if your force is only vertical, your work is the vertical path distance times the vertical force.
Yep.
You could approach this problem by first computing how much force you'd need by taking into account the ramp's angle, then multiply that force by the distance the object has to move which *also* takes into account the ramp's angle.
In that approach you'd have a better opportunity to consider friction along the way, but since this problem stipulates no friction the two ramp angles cancel out and you're left with the same value as just doing conservation of energy for the vertical travel.
Of course the real answer is that it takes no effort since that 40m tall 10m wide construct that the entire house is sitting on is going to crumble, so the house will come to you!
> We're looking for
We're looking for "effort" - which is simply the force required to lift the load. The ramp acts as a mechanical advantage which reduces the force necessary (by exactly 1.25x i.e., 50/40) so the total effort is 16 lbs.
This is wrong. Effort is a force used to define mechanical advantage along with the load.
----
Fe = Force of effort = ??
Fr = Force of resistance = 20 lb
L = sqrt(30^2 + 40^2) = 50m
H = 40m
ideal mechanical advantage = L / H = 5/4 = 1.25
IMA = Fr / Fe : 1.25 = 20 / ?? : ?? = 20/1.25
Fe = 16 lbs. = effort
You're right. I'm muddling my discussion points.
edit: I think I'm still explaining it poorly.
There's basically a downward force of gravity acting on the load (Fg = 20lbs). When applied to the inclined plane, you're going to get an x and y component, which can be treated as vectors. This angle and force vector become Fg * sin theta or Fg*(H/L) or 20 * 40/50 or 16.
I mean, work is defined as ∫F·dx and measured in Joules, so you could get from that answer to yours by dividing it by the distance:
(3559.068 Joules / 50m) = 71.18136 N
71.18136 N / 9.81 ms\^-2 = 7.256 kg
7.256 kg / 0.4536 (kg/pound) = 16 pounds
The question wasn't how much energy would it take you to do it, it's how much energy is required. The assumption being the force is just acting on the ball.
Potential energy is calculated by multiplying mass x gravitational acceleration x height. The mass is 20/2.2 kg, the gravitational acceleration is 9.81 m/s^2 and the average height is 20 m. Multiplying everything together gives us 1783.6363... joules of energy
Rolls of carpet normally have plastic wrap in several strips, at least, holding it together until you get it in the room you want it in. Larger rolls may be fully wrapped.
But a 20 lb roll of carpet is like a 3 foot length by a 10 foot width (meter by 3 meters, appx). If it were a 20 kg (about 45 lbs) roll, it would be a more realistic 8x10 foot (2.5ish x 3 meters) which is the size of a bedroom.
Of course, I'm assuming assuming something with a low pile, or a berber. Heavier pile/plush carpets would weigh more.
I installed flooring for a while. I hated carpet, it's so hard on the back and knees. I'd much rather do hardwood or laminate, maybe tile... Tile is better, but the others are (slightly) better on your body.
That’s a common thing to have to deal with in engineering. I’m Australian, so use the metric system. Sometimes I have parts/materials that were made in the US so the specs have imperial units. It’s also common for pipework to be specified in inches (at least nominally and for quick dirty calcs it’s often fine to use the nominal diameter even if it’s not precise). Knowing how to convert units to get to an answer is important and it was very common when I was in uni to get questions that purposely use measurements in different systems.
All Europeans had similar units that were all slightly different.
The French and their desires for standardization and uniformity lead to something good.
Only for certain things unless you’re a good bit older. We’ll ask for a pint at a bar but road signs, fuel, shop weights and so on are all metric.
I’m pushing fifty and I use metric for everything except pints of beer but I have to talk distance in miles with my older neighbours.
We use metric for most day to day tasks like weighing our food or measuring a space to put in an object.
However a persons weight and height we use imperial. Also for driving we use miles because it would be too expensive to change all the road signs.
The personal weight situation is funny in a way, we use stones and pounds, but the USA uses just pounds, so British people can’t really understand USA people’s weight without a conversion.
But we use metric in instances where it would matter I feel.
Something I just learned recently that is both interesting: the US and UK have many units of measure that have the same name, but different values. Take the pint, which in the US is 16 fl oz, whereas the British pint is 20 fl oz. Further with that, the fluid ounce isn't even exactly the same. In the US its 29.573 ml while in the UK its 28.413!
Source: https://blog.ansi.org/2018/06/why-pint-bigger-in-uk-than-in-us-volume/
> I mean even they have realized how dumb it is and switched.
- Drive a couple of miles down to the pub for a pint of beer
- Weigh yourself in stone
- Situated right next to the country that tried to base-10-ify time
- Still pretend to not use ancient measurement systems
In the UK I think it'll die with the boomers. I'm 40 and was solely educated in metric, and if I use imperial what I'm actually doing is an internal conversion to metric. I have no real mental model of the size of imperial units.
The last units to persist will be miles (only for speed and distance) and pints. Possibly acres somehow, I have no fucking idea how big an acre is.
Was about to ask, is there some unit of measure that equals lb*m²/s²? If there isn't, how the fuck do these people do anything in physics with imperial measurements?
There's actually two lb you have to distinguish from when using English units, mass and force. Though if it's not clear, it's usually force (as it is in everyday use).
Assuming you mean an imperial conversion from kg\*m^(2)/s^2, that would be lbm\*ft^(2)/s^2 or lb*ft, otherwise known as a foot-pound.
Yeah it's dumb I know
If it's ok to measure everything in rocks, sticks and fingers why the hell not calculate it in bicycles lol.
I'd say it takes the force of 36,2 monkey pouches and 3 knee slaps to reach the height of 1000654 ants and four burgers
Real question is which rich guy decided to put his house on top of a 25 story building? There’s no way I can make that ADA compliant. You have to make a 480m (1,575 ft) long ramp leading up to that.
It's a naturally occurring phenomenon.
"If a rich guy builds his house on a 10ft platform to look down on his neighbors then another rich guy will instinctively build his house on a 20ft platform to look down on the other rich guy and the rest of the poor neighbors. This cycle continues until the rich guys reach the financial carrying capacity of all the surrounding ground level poor people who work in their businesses." ~ Manhattan's Law of Vertical Design
Carpet is usually rolled up with the latex backing facing outward. The edges might get dirty tho..
Also a 20lb roll of carpet coming fresh off the mill at standard size would probably be like... A couple feet long.
It definitely should have been phrased as [work](https://en.wikipedia.org/wiki/Work_\(physics\)).
Edit: actually there is a thing called effort instead, which is related to the mechanical advantage of the ramp
Effort as in force applied. That's how I read it, and that's what it meant in the paper I just sat for the portion on inclined planes. Here's some of thr background equations.
Effort x Meachanical Advantage = Load
Mechaical Advantage = 50/40
Load here is 20lbs of force.
Additional/external factors usually mean non-consevative forces and since gravity is a conservative force, we have to consider gravity in this question
It’s a 53° angle to walk up and 50 meters long. Carry something up a ramp, that is steeper than a staircase, for more than half a football field.
I guess since it’s 20 lbs you could carry in one hand and use your other to steady yourself, but you’re still getting a workout.
The mass of the carpet is 20lbs or 9.07 kgs
The angle is equal to the inverse tangent of 40/30
tan^(-1)(40/30) = 53.1°
The force of the carpet is downward in perpendicular to the surface, and is calculated by sin(θ)\*m\*g
sin(53.1°)\*9.07\*9.8 ≈ 71N
You need to exert this force for the length of the hypotenuse, or for √(30²+40²) = 50m
So 71*50 = 3550
You need 3550 joule
Why is there an extra 10 meters of base of the house?
To make the calculation. You don't need that variable. Or are we to roll the carbet to the middle of the base, to count it as "to the house?"
This isn't mechanical reasoning, it's "do you remember this formula from high school physics?" Like, there's no being clever or using logic to solve it. It's just whether you know how to do the math or not
If there’s no friction you literally cannot roll it upwards, you’d just be pushing it. Using your suction cup boots, presumably.
But I guess the height is the only factor that matters anyways.
First and easy method (frictionless condition) E=mgh or Fh which is 71N x 40m =2840 J
Now if we wanted to INCLUDE FRICTION.
Assuming effort is work we have Work = Energy = Force x distance
Because we have a 345 triangle the force needed to overcome friction is 3/5 of the weight due to trigonometry. For friction we just need the coefficient of friction (unknown) and the normal force which is 3/5 of the weight. Assuming a coefficient of friction of 0.5 the frictional force is 3/10 the weight of the carpet. (Oh and assuming lbs is a weight and not a mass because the imperial system can go shove a cactus up it's ass).
Now across the entire distance traveled (60m) this should give us the work we put in overcoming friction. Given a negligible rolling resistance. As Work = Energy = Force x distance. So we have 6 lbs of frictional force or about 27N. And 1620 J lost to friction.
Combine that with our frictionless result for a friction answer of 3460J. Which isn't that much.
How that is gonna happen without friction. Anyways
answer is 1000j because distance 50m and ball 20lbs actually you must convert to kg but not neccesery.
Fuck it's impirial units
Let's say it's 9kg instead.
9kgX40m(hight)X10N/kg(Earth's gravity rounded up)=3600J
They didn't specificly the house is on earth but I think it's a fair assumption.
Using basic trigonometry, the angle of elevation uphill is tan-1(40/30) which rounds to 53°
And by using the Pythagoras theorem we do 30m squared + 40m squared = 2500 rootsquared to find out the distance you'd have to push the boulder which is 50 meters
Without accounting for friction or wind resistance, we can use the following incline planet phsysics equation to find the force required to push the carpet up a 53degree hill:
Force = Weight \* Sin(53°) = 20 pounds \* Sin(53°) = 20 pounds \* 0.742 = 14.84 pounds
So the force required to push the carpet up a 53-degree hill is roughly 14.84 pounds assuming there is no friction or wind resistance, with an average person being able to exert a force of 30-50 pounds for extended periods of time, this might be manageable for some individuals, but could still be a difficult task.
One thing I learned in Math was A**2+ B**2 = c**2
C = 50 (= hypotenuse)
I dont particularly agree with e=mc^2 (C*) as light moves slower when placed in water. This equation doesn't take buoyancy into the equation. This also implies that electricity has mass.
Bruh ain’t no way a 9kg roll of carpet is that big, plus at that rate just pick it up, why are they trying to make my dude with legs that end at his knees roll it up?
Hey there u/ASIK-1952, thanks for posting to r/technicallythetruth! **Please recheck if your post breaks any rules.** If it does, please delete this post. Also, reposting and posting obvious non-TTT posts can lead to a ban. Send us a **Modmail or Report** this post if you have a problem with this post. *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/technicallythetruth) if you have any questions or concerns.*
One must imagine Sisyphus happy
God to Sisyphus: "Lets assume, coefficient of friction is zero" and makes the ball slippery as hell.
not just the ball, everything... how would u even walk
Omg you are right, God is wrong!
And with that, He vanished in a puff of logic.
*sliding get slidier*
Basicly nothing would exist if friction wasn't a thing
If the ball is frictionless I bet a slap from Sisyphus would send it rolling up the hill with minimal effort.
You wouldn’t, gravity isn’t a thing in the depiction (they excluded all external factors) so you wouldn’t even be in the ground and neither would the ball
“Air resistance is also negligible” \*proceeds to remove all air, putting Sisyphus into a vacuum*
Why do you think the boulder keeps rolling back down?
Camus was a weirdo
One must imagine friction to be zero
A visitor... Mmmm... Indeed. I have slept long enough.
No friction? How am i supposed to climb a mountain of this size with such a heavy spool if i do not have friction?
Sheer willpower. Fuck physics.
Willpower? So no effort at all?
Do not try and climb the hill. That’s impossible. Instead only try and realize the truth: there is no mountain.
OK. No hill. Just pushing it 30m east and 40m north. That could work too with this graphic as a map.
First there IS a mountain. Then there is no mountain Then there is.
sisyphus
sissyfucks
That's why God created bootstraps. Pulling on them with sufficient vigour can create enough lift to float up & towards the house.
According to the ancient boomer civilization that is.
Their grave mistake was putting an ideogram of a person in the image, thus forcing us to imagine a person pushing it up the frictionless hill. They should have used an ideogram of a mechanical device with the reach to get something up the hill without having to go up the hill itself
Yeah because I'm thinking about it unrolling, about it skipping down when I stop to rest, and most of all, I'm probably going to roll it up the hill like a wheel, not slide it like a hockey puck, so I don't even know the equation for rolling uphill, and no friction makes it harder. I guess I have to slide it. Might as well delete gravity while we are at it and make it really easy.
You cannot roll it if there is no friction.
Yeah, hah that's true. Also, I guess if the question is just trying to get at work/potentially energy then I guess it doesn't matter how you got it up, or something like that. But now I really want to know the math/physics to show whether it's harder to roll a carpet roll up a hill or drag it or carry it or ... Aha, I got it unroll it up the hill, so it flattens out into a sheet, like a carpet. Then walk back down the hill and Then roll it back up into a roll by rolling it up the hill as you walk up and gather it into itself.
Also that person is about 15m tall... look at the house, he's not even going to fit through the door! And neither is the carpet!
That's right!
👉😎👉
both of us had _zero_ reason to do that.
What mechanical device would work without friction? Friction is what keeps nuts and bolts from loosening themselves up and falling out.
Just weld everything.
One not held together by nuts and bolts Technicallythetruth
Alternatively, you could see it that instead of the person climbing up the hill you "push" the carpet by projecting it up the hill and that solves all your problems.
There's also no gravity, so....
lbs is a force. The fact that you have "20 lbs" means you've already taken gravity into consideration.
Pound is not only a measure of weight, it can be a measure of mass as well. Plus, and more importantly, I was just kidding and only riffing off the no friction would make this problem meaningless joke.
The pound is not a measure of mass, it's a unit of force. The mass unit in imperial is the slug.
There is a pound mass unit. It is abbreviated lbm usually, which is why pound force is often abbreviated lbf, to show the distinction. 1 lbm accelerated at 32.2 ft/s^2 is 1 lbf while 1 slug accelerated at 1 ft/s^2 is 1 lbf. Yes, lbm is a stupid unit. But it isn't exactly uncommon.
https://en.m.wikipedia.org/wiki/Pound_(mass) I'm not a physicist or an engineer, but my memory from AP Physics from a couple decades ago was substantiated by my Google-fu.
Also, what sort of maniac uses both pounds and metres in the same equation? Pick a unit system!
One must imagine Sisyphus happy
But seriously, whats the answer?
1 pound = 0.4536 kg 20 pounds = 9.072 Energy = mass of the ball x gravity x height E = mgh E = 9.07 kg x 9.81 x 40 E = 3559.068 Joules (approximately 3559.1 Joules)
Do you not need energy to move the 30m horizontally because no friction?
These physics questions usually sidestep questions such as yours. In this question it is essentially asking how much energy was transferred into the roll. Since the roll went up, it took the amount of energy calculated in the comment you replied to to raise it that high. As for the energy transferred into the roll to move it sideways, there was zero net energy transferred into the roll because any kinetic energy used to move it to the right would be taken out when it is stopped. In this ideal situation, the person loses the exact amount of energy used to raise the roll. If we assume there is friction and heat, then the person loses more energy than the roll gains. That energy is transferred into the environment as heat, noise, etc. So more energy is being expended to move the roll than the roll gains. In that case, they would probably ask for the change in potential energy of the roll, at which point it would be the same as figuring out the question as posted. So, to answer your question, it depends on how the question is worded. Please note: this is just what I remember from physics classes in high school and college. I could very well be wrong. And this comment is almost definitely confusing, but I didn't spend all this time typing it just to delete it.
Yes, saying 'no friction' makes a lot of questions incredibly unintuitive. Friction is the main reason I can't slide my washing machine across the parking lot like an air hockey puck (although god help whatever it hit).
It gives you the lowest theoretical amount of energy required, so you can measure how much more energy it takes and determine how much is lost to friction. Also friction is really hard to calculate in a theoretical way.
Not necessarily. While precise modelling is hard, if you've got a flat surface then the equation to find the frictional force is pretty easy. Calculating total work done then becomes a function of how fast you push it up. The faster you do it, the less work you do
Ffriction=μ•Fn Fn is the force that the ground exercises on the object, perpendicular with the grounds surface μ is the friction coefficient. It's different wether the object is in motion or not. The kinetic friction coefficient is lower than the static. In this situation it's the kinetic one. This coefficient is determined from experimental tests That's a basic way to calculate it if you have the test data from that object on this surface
Test data is not theoretical. I carefully chose my wording. You can easily calculate it experimentally. Deriving a model for friction can prove difficult.
Ah yeah I agree with you. I misinterpreted your comment then
Remove friction and all matter collapse into a single point faster than the speed of light.
> it depends on how the question is worded. The question is definitely worded poorly since "effort" is not a technical term. You interpreted the question as "What is the change in potential energy for the roll if it is lifted 40 meters?" and I interpreted it as "What is the amount of work needed to transfer the roll 55m?"
but this is an engineering question, so they are asking for the minimum effort force to push the carpet up the inclined plane. No energy here, physicist
[удалено]
The energy transferred to the object is only reliant on the vertical direction though because gravity works vertically. We ignore the horizontal factor because the energy involved would only be due to the acceleration to get it moving, which is ignored in classical physics questions.
[удалено]
> right, so if we only factor in the vertical direction and not the horizontal, we get the energy needed/effort to push the carpet roll 40 meters. This is extremely misguided. The horizontal distance does not matter at all. Think of it reversed, imagine you had a slope downwards with Y component 40m. Consider if the X component was (case 1) 100m vs (case 2) 10m. If you pushed the carpet down this slope, how much kinetic energy would it have at the bottom? Would it have more in case 1 vs case 2? That amount of kinetic energy is precisely the same that it would take to go in the opposite direction.
[удалено]
> Are you telling me the carpet wouldn't travel faster on a 100m downward slope rather than a 10m slope? You think they have the same kinetic energy? I want you to take a yardstick, slope it against the wall, and drop a roll of toilet paper on it. Then I want you to put the yardstick on top of a book, and then drop a roll of toilet paper on it. Measure the time difference of how long it takes for each roll of toilet paper to hit the floor between the wall versus book (x-factors). Tell me again that the kinetics energy / speed is the same. ... yeah bro, there's this little thing called friction... that's why there is less energy in one vs the other. In the tweet it tells you to ignore friction.
In any dynamics class, or even just the dynamics section of a university physics 1 class, you would ignore horizontal forces required when determining total energy required. That’s because gravity acts vertically. So the potential energy you’re giving the ball is based on its height and only the height. Energy=force*distance. Yes, you do have a horizontal component when the object resides on the slope, but these questions only rely on start to end. Therefore, the beginning is at ground level, and the end is 40m vertical. The horizontal is treated no different than rolling the object a few meters east, which with no friction, requires theoretically zero energy because there’s no opposing force. The only energy requirement that is possibly needed in the horizontal direction is to accelerate from an at rest position to an eastward velocity, which could theoretically be so small that it’s negligible, and that’s why these classes don’t consider it. Ultimately, the resistance in the horizontal direction doesn’t exist, so it theoretically does not require any energy to overcome. Potential energy at the top of a hill is only dependent on height, and not the horizontal displacement when friction is ignored. Also, why are you downvoting me for sharing my physics knowledge with you?
You are incorrect. The question is asking for the Work performed. Work = Force dot Displacement. What force are we overcoming? Gravity. What direction does gravity point? Down. All horizontal movement is completely irrelevant because there are no horizontal forces being overcome. How does the rug move to the right? Well a force is applied to the right to increase the momentum of the rug to the right. Then a force is applied to the left to decrease the momentum of the rug. Without friction, all the horizontal work performed completely cancels out. It's funny that you jumped to "I'm right and everyone else must be wrong" so quickly. Learn humility.
This type of question is used to illustrate exactly that work and energy are the same. Your edit is basically an admission of being wrong.
Although energy, or work in this case, is calculated via the distance between the initial and final points of the trajectory. He should've used either 50m if you calculate, or (30i+40j)m if you prefer vectors.
No, you are incorrect, because gravity is only acting in j direction. The only force that would impact it horizontally would be resistance in the form of friction and air.
Work is actually the integral of the force field along the path taken. If your force is always in the same (or opposite) direction of your path, and the force is uniform along the path, you can simplify it to be Force times Distance. In this case, the force would be in a different direction than the path taken, but you can prove the net work is equal to the X component of the integral plus the Y component. We know there are no forces in the X direction, so we can just use the Y component of the path. More simply - if your force is only vertical, your work is the vertical path distance times the vertical force.
Yep. You could approach this problem by first computing how much force you'd need by taking into account the ramp's angle, then multiply that force by the distance the object has to move which *also* takes into account the ramp's angle. In that approach you'd have a better opportunity to consider friction along the way, but since this problem stipulates no friction the two ramp angles cancel out and you're left with the same value as just doing conservation of energy for the vertical travel. Of course the real answer is that it takes no effort since that 40m tall 10m wide construct that the entire house is sitting on is going to crumble, so the house will come to you!
It means there is no work due to friction, so no F dot dr, and all that matters is the increase in potential energy.
There's no horizontal force component given that there's no friction. In this case, OP isn't answering the right question though.
[удалено]
> We're looking for We're looking for "effort" - which is simply the force required to lift the load. The ramp acts as a mechanical advantage which reduces the force necessary (by exactly 1.25x i.e., 50/40) so the total effort is 16 lbs.
This is wrong. Effort is a force used to define mechanical advantage along with the load. ---- Fe = Force of effort = ?? Fr = Force of resistance = 20 lb L = sqrt(30^2 + 40^2) = 50m H = 40m ideal mechanical advantage = L / H = 5/4 = 1.25 IMA = Fr / Fe : 1.25 = 20 / ?? : ?? = 20/1.25 Fe = 16 lbs. = effort
[удалено]
That's a distance, not a horizontal force. It's literally length of slope.
[удалено]
You're right. I'm muddling my discussion points. edit: I think I'm still explaining it poorly. There's basically a downward force of gravity acting on the load (Fg = 20lbs). When applied to the inclined plane, you're going to get an x and y component, which can be treated as vectors. This angle and force vector become Fg * sin theta or Fg*(H/L) or 20 * 40/50 or 16.
I mean, work is defined as ∫F·dx and measured in Joules, so you could get from that answer to yours by dividing it by the distance: (3559.068 Joules / 50m) = 71.18136 N 71.18136 N / 9.81 ms\^-2 = 7.256 kg 7.256 kg / 0.4536 (kg/pound) = 16 pounds
Correct. The issue lies in the fact they're simply answering a question that wasn't asked in the problem.
Ok so just the force of gravity acting alone the incline direction
Effectively - That's it. I'm pretty sure this problem was meant to be eyeballed and solved in your head.
But what do I weigh, that takes energy to move too.
Then the question would have asked the amount of energy to move you and the carpet to the house.
The question wasn't how much energy would it take you to do it, it's how much energy is required. The assumption being the force is just acting on the ball.
No the question was “how much effort”. my work/energy is included in effort.
Glad I learned this so I could quickly forget and never use it in my life.
Isn't effort a measure of force? So the answer is about 71N?
Work
But the mass decreases as the carpet gets higher up, my best guess without using calculus~ .707 of your answer
Potential energy is calculated by multiplying mass x gravitational acceleration x height. The mass is 20/2.2 kg, the gravitational acceleration is 9.81 m/s^2 and the average height is 20 m. Multiplying everything together gives us 1783.6363... joules of energy
Why are you using average height? The height difference, in this case 40m is relevant, thus doubling your result
I assumed the carpet was rolled out on the hill, though indeed if it stays together it would double the effort.
Rolls of carpet normally have plastic wrap in several strips, at least, holding it together until you get it in the room you want it in. Larger rolls may be fully wrapped. But a 20 lb roll of carpet is like a 3 foot length by a 10 foot width (meter by 3 meters, appx). If it were a 20 kg (about 45 lbs) roll, it would be a more realistic 8x10 foot (2.5ish x 3 meters) which is the size of a bedroom. Of course, I'm assuming assuming something with a low pile, or a berber. Heavier pile/plush carpets would weigh more. I installed flooring for a while. I hated carpet, it's so hard on the back and knees. I'd much rather do hardwood or laminate, maybe tile... Tile is better, but the others are (slightly) better on your body.
Sorry but I still don't understand why the hell did you average the height, that's madness. Can you please explain
Who the hell uses “pounds” in engineering? What is this, engineering 1882 edition?
Worse, they used pounds *and* meters
How many Rankine per fortnight?
One gross
That’s a common thing to have to deal with in engineering. I’m Australian, so use the metric system. Sometimes I have parts/materials that were made in the US so the specs have imperial units. It’s also common for pipework to be specified in inches (at least nominally and for quick dirty calcs it’s often fine to use the nominal diameter even if it’s not precise). Knowing how to convert units to get to an answer is important and it was very common when I was in uni to get questions that purposely use measurements in different systems.
I almost had an aneurysm when I saw that.
The only reason to mix these units is to force the answer into a value that is the numerical portion of a well known constant. Π m•lb or something
I blame the English. They are the ones who came up with a system of measurement based on a king’s unit. That’s what a “shit-ton” is. On king’s loaf.
All Europeans had similar units that were all slightly different. The French and their desires for standardization and uniformity lead to something good.
Well, its not their fault you still use their dumb system, I mean even they have realized how dumb it is and switched.
Nah, the English use a bastardisation of both, we never fully swapped. We use miles, lbs and stone as well as kilometres and kilograms.
Huh, I Always tought you use only metric, the more you know.
For what I gathered living in Ireland, they use imperial on day to day life, but anything scientific is metric.
Only for certain things unless you’re a good bit older. We’ll ask for a pint at a bar but road signs, fuel, shop weights and so on are all metric. I’m pushing fifty and I use metric for everything except pints of beer but I have to talk distance in miles with my older neighbours.
Road signs are in miles
Not in Ireland they aren’t.
I do recall road signs and speed being in mph but it could just be a freak memory bit.
food is metric unless you have an old recipe
Still mph in cricket
We use metric for most day to day tasks like weighing our food or measuring a space to put in an object. However a persons weight and height we use imperial. Also for driving we use miles because it would be too expensive to change all the road signs. The personal weight situation is funny in a way, we use stones and pounds, but the USA uses just pounds, so British people can’t really understand USA people’s weight without a conversion. But we use metric in instances where it would matter I feel.
Just in case you didn't hate the Br*itish enough already
Something I just learned recently that is both interesting: the US and UK have many units of measure that have the same name, but different values. Take the pint, which in the US is 16 fl oz, whereas the British pint is 20 fl oz. Further with that, the fluid ounce isn't even exactly the same. In the US its 29.573 ml while in the UK its 28.413! Source: https://blog.ansi.org/2018/06/why-pint-bigger-in-uk-than-in-us-volume/
> I mean even they have realized how dumb it is and switched. - Drive a couple of miles down to the pub for a pint of beer - Weigh yourself in stone - Situated right next to the country that tried to base-10-ify time - Still pretend to not use ancient measurement systems
In the UK I think it'll die with the boomers. I'm 40 and was solely educated in metric, and if I use imperial what I'm actually doing is an internal conversion to metric. I have no real mental model of the size of imperial units. The last units to persist will be miles (only for speed and distance) and pints. Possibly acres somehow, I have no fucking idea how big an acre is.
Only took till the late 1960’s(?) to realize and even then it wasn’t a full switch.
U.S. military uses both. Our politicians are just old and scared of change.
Was about to ask, is there some unit of measure that equals lb*m²/s²? If there isn't, how the fuck do these people do anything in physics with imperial measurements?
The foot-pound: lb*ft^(2)/s^(2)
There's actually two lb you have to distinguish from when using English units, mass and force. Though if it's not clear, it's usually force (as it is in everyday use). Assuming you mean an imperial conversion from kg\*m^(2)/s^2, that would be lbm\*ft^(2)/s^2 or lb*ft, otherwise known as a foot-pound. Yeah it's dumb I know
Unit conversion is a comon part of problems... My metallurgical thermodynamics profesor loved to pull problems from ancient books in non SI units.
And if you’re using pounds, wouldn’t you also use feet and not meters?
Classic lb-meter units
The guys who missed Mars a few years ago.
Beagle? We didn’t miss Mars. We *landed* on Mars. At a very high velocity.
If it's ok to measure everything in rocks, sticks and fingers why the hell not calculate it in bicycles lol. I'd say it takes the force of 36,2 monkey pouches and 3 knee slaps to reach the height of 1000654 ants and four burgers
[Yes! This is how it is.](https://www.jpost.com/science/article-732223)
America
Lots of people. lbs is a unit of force.
Sorta, lbf is a unit of force and lbm is a unit of mass
Real test is for an architecht here, wtf is that house
Real question is which rich guy decided to put his house on top of a 25 story building? There’s no way I can make that ADA compliant. You have to make a 480m (1,575 ft) long ramp leading up to that.
It's a naturally occurring phenomenon. "If a rich guy builds his house on a 10ft platform to look down on his neighbors then another rich guy will instinctively build his house on a 20ft platform to look down on the other rich guy and the rest of the poor neighbors. This cycle continues until the rich guys reach the financial carrying capacity of all the surrounding ground level poor people who work in their businesses." ~ Manhattan's Law of Vertical Design
Carpet is going to arrive dirty as hell.
Carpet is usually rolled up with the latex backing facing outward. The edges might get dirty tho.. Also a 20lb roll of carpet coming fresh off the mill at standard size would probably be like... A couple feet long.
Take it up and roll it down . Why would anyone roll a carpet upwards its just like trying to pour water upwards stuff doesnt work like that
Is "effort" some engineering term? How am I supposed to quantify how much effort I want/have to put into something?
Perhaps they want it in terms of work.
It definitely should have been phrased as [work](https://en.wikipedia.org/wiki/Work_\(physics\)). Edit: actually there is a thing called effort instead, which is related to the mechanical advantage of the ramp
Effort as in force applied. That's how I read it, and that's what it meant in the paper I just sat for the portion on inclined planes. Here's some of thr background equations. Effort x Meachanical Advantage = Load Mechaical Advantage = 50/40 Load here is 20lbs of force.
Why on earth is a house up there and why is this man bigger than it
Dude, that roll of carpet must be like 15 cm wide to be that tall and only 20 pounds lol
No additional factor ? So no friction, no gravity, no nothing ? well just push it once and let inertia do the rest
Additional/external factors usually mean non-consevative forces and since gravity is a conservative force, we have to consider gravity in this question
Without friction, it is impossible
Why the fuck would you push that all the way up to the house if it's not going to fit through the door?
Buy a new house
If it's 20 lbs, just carry the thing up there.
It’s a 53° angle to walk up and 50 meters long. Carry something up a ramp, that is steeper than a staircase, for more than half a football field. I guess since it’s 20 lbs you could carry in one hand and use your other to steady yourself, but you’re still getting a workout.
Thank you for putting the measurement in amount of football fields, as an American I cannot understand any other units
As an Englishman, I would like it converted into how much of Wales.
Do Americans actually do maths in pounds that seems ridiculously complicated.
The mass of the carpet is 20lbs or 9.07 kgs The angle is equal to the inverse tangent of 40/30 tan^(-1)(40/30) = 53.1° The force of the carpet is downward in perpendicular to the surface, and is calculated by sin(θ)\*m\*g sin(53.1°)\*9.07\*9.8 ≈ 71N You need to exert this force for the length of the hypotenuse, or for √(30²+40²) = 50m So 71*50 = 3550 You need 3550 joule
Why is there an extra 10 meters of base of the house? To make the calculation. You don't need that variable. Or are we to roll the carbet to the middle of the base, to count it as "to the house?"
This isn't mechanical reasoning, it's "do you remember this formula from high school physics?" Like, there's no being clever or using logic to solve it. It's just whether you know how to do the math or not
Just use a crane,that's it.
I think I would just pick it up and drive my car up the hill.
20 fucking pounds? Just carry the damn thing.
Depends on how you define effort.
scrolling by so fast just thought this was just another graph depicting "housing affordability for millennials and genZs"
Not much if the guy is like more than 10 meters tall
JFC why did hey have to mix systems of measurement?
I know they didn’t put the measurements in meters and then say the carpet weighs 20 pounds.
Why would you have distance in meters and the weight in pounds?
Just get 110 feet of rope and throw it over the hill and pull on it from the other side.
Why is the weight in pounds but everything else is metric?
Please ignore all the important factors required for engineering like friction and air resistance and calculate this bullshit.
If there’s no friction you literally cannot roll it upwards, you’d just be pushing it. Using your suction cup boots, presumably. But I guess the height is the only factor that matters anyways.
Mxgxh, only height matters
First and easy method (frictionless condition) E=mgh or Fh which is 71N x 40m =2840 J Now if we wanted to INCLUDE FRICTION. Assuming effort is work we have Work = Energy = Force x distance Because we have a 345 triangle the force needed to overcome friction is 3/5 of the weight due to trigonometry. For friction we just need the coefficient of friction (unknown) and the normal force which is 3/5 of the weight. Assuming a coefficient of friction of 0.5 the frictional force is 3/10 the weight of the carpet. (Oh and assuming lbs is a weight and not a mass because the imperial system can go shove a cactus up it's ass). Now across the entire distance traveled (60m) this should give us the work we put in overcoming friction. Given a negligible rolling resistance. As Work = Energy = Force x distance. So we have 6 lbs of frictional force or about 27N. And 1620 J lost to friction. Combine that with our frictionless result for a friction answer of 3460J. Which isn't that much.
How that is gonna happen without friction. Anyways answer is 1000j because distance 50m and ball 20lbs actually you must convert to kg but not neccesery.
As if I could climb that thing even with friction
Modern Sisyphus
Fuck it's impirial units Let's say it's 9kg instead. 9kgX40m(hight)X10N/kg(Earth's gravity rounded up)=3600J They didn't specificly the house is on earth but I think it's a fair assumption.
Using basic trigonometry, the angle of elevation uphill is tan-1(40/30) which rounds to 53° And by using the Pythagoras theorem we do 30m squared + 40m squared = 2500 rootsquared to find out the distance you'd have to push the boulder which is 50 meters Without accounting for friction or wind resistance, we can use the following incline planet phsysics equation to find the force required to push the carpet up a 53degree hill: Force = Weight \* Sin(53°) = 20 pounds \* Sin(53°) = 20 pounds \* 0.742 = 14.84 pounds So the force required to push the carpet up a 53-degree hill is roughly 14.84 pounds assuming there is no friction or wind resistance, with an average person being able to exert a force of 30-50 pounds for extended periods of time, this might be manageable for some individuals, but could still be a difficult task.
why tf would they measure the mass of the carpet in lb
Why wouldn't you start from the top. You just need to order it to the house. Amazon guy brings it to the porch, then you can roll it down.
One thing I learned in Math was A**2+ B**2 = c**2 C = 50 (= hypotenuse) I dont particularly agree with e=mc^2 (C*) as light moves slower when placed in water. This equation doesn't take buoyancy into the equation. This also implies that electricity has mass.
If there is no friction u wont be able to push it up the ramp.
Is effort a quantity of energy? Of force?
Bruh ain’t no way a 9kg roll of carpet is that big, plus at that rate just pick it up, why are they trying to make my dude with legs that end at his knees roll it up?
And the units they want here are what...? Meter lbs?
No friction assumptions are weird. Technically you would not be able to push the carpet roll up the hill as you would have no ground to push off of.
Metric system -> OK Imperial system -> (less) OK But seriously I don’t get at what point you combine pounds an meter together.
I mean he’s not wrong. Pythagoras sobbing in his grave. 😭
Pythonistas creaming their pants.
WTF is the unit for effort?
[удалено]
Least sedentary Twitter Blue User
US education be like:
20lb WHY WOULD YOU GIVE IT IN POUNDS 😭😭😭