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Work done by friction Help!

by Chica1975
Tags: friction, work
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Chica1975
#1
Oct1-10, 04:53 PM
P: 63
I have a physics teacher who is unable to explain anything if his life depended on it hence I am really struggling with physics. I am left out on a limb literally - at my wits end.

I have this question that I have no idea where to start with.

2 villans slid a laundry basket containing a body a distance of 7.76m across a warehouse floor. They both exerted equal horizontal forces of 319N in order to keep the basket moving at a constant velocity of 1.52m/s. How much work was done by friction?

Please explain to me step by step why we get to the answer please don't just give me the equations and the answer I need to understand why we get there. I did math 20 years ago so its a whole new ball game for me.

Thanks
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berkeman
#2
Oct1-10, 05:10 PM
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Quote Quote by Chica1975 View Post
I have a physics teacher who is unable to explain anything if his life depended on it hence I am really struggling with physics. I am left out on a limb literally - at my wits end.

I have this question that I have no idea where to start with.

2 villans slid a laundry basket containing a body a distance of 7.76m across a warehouse floor. They both exerted equal horizontal forces of 319N in order to keep the basket moving at a constant velocity of 1.52m/s. How much work was done by friction?

Please explain to me step by step why we get to the answer please don't just give me the equations and the answer I need to understand why we get there. I did math 20 years ago so its a whole new ball game for me.

Thanks
Welcome to the PF.

What are the relevant equations for calculating work from force and distance? What is the total force in this question? What is the distance?
Chica1975
#3
Oct1-10, 05:24 PM
P: 63
Thanks

W = F*d cos theta
total force is 638
distance is 7.65m

berkeman
#4
Oct1-10, 05:27 PM
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Work done by friction Help!

Quote Quote by Chica1975 View Post
Thanks

W = F*d cos theta
total force is 638
distance is 7.65m
Good. And since the question says that the forces are applied horizontally (parallel with the direction of motion), what are theta and cos(theta)? And your final answer (including units) is..... ?
Chica1975
#5
Oct1-10, 05:29 PM
P: 63
theta and cos theta (I think) should be 0 because they are parallel?
I did do this and got an answer of 4880.7 Joules - should be negative because friction is going in the opposite direction.

their answer is -4.95 KJ even if I divide by 1000 I still don't get the right answer.
berkeman
#6
Oct1-10, 05:36 PM
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P: 41,144
Quote Quote by Chica1975 View Post
theta and cos theta (I think) should be 0 because they are parallel?
I did do this and got an answer of 4880.7 Joules - should be negative because friction is going in the opposite direction.

their answer is -4.95 KJ even if I divide by 1000 I still don't get the right answer.
Sorry, I missed a typo in your previous post. The distance in the original problem in your first post is 7.76m, not 7.65m. That accounts for the small difference between your answer and theirs.

BTW, you should have said theta = 0, so cos(0) = 1. That must be what you meant, since you would have gotten the right answer without the distance typo.

Good job.
Chica1975
#7
Oct1-10, 05:40 PM
P: 63
thanks a mil - sometimes you just need guidance to get your confidence and when you have been looking at it for hours without success it gets harder and harder.


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