Calculate the work done by friction

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  • #1
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Homework Statement


You have a level track. You push a cart with mass = 1.12[kg].
You measure the initial velocity to be 0.57[m s-1].
2 seconds later, you measure the velocity to be 0.427[m s-1].


Homework Equations


What is the work (reported in mJ) that friction did on the cart?


The Attempt at a Solution



W(f)=F(f) x d

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
SammyS
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Welcome to PH.

You need to show us your work so we can help you.

Hint: What does the Work-Energy Theorem say?
 
  • #3
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W= deltaK = 1/2m(Vf^2 - Vi^2)

W=1/2 (1.12kg) [((0.427m/s)^2) - ((0.57m/s)^2)]

W= -0.0798 kg m/s

Is this the work done by friction though? or the cart?
 
  • #4
SammyS
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On what object would the cart do work?

Friction slows the cart, so it does negative work on the cart, so your answer seems reasonable.
 
  • #5
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Okay that makes sense. thank you.

So if i were to calculate work done by friction, but this time I'm given distance and delta K, would I use Wncf=fd where f=(deltaK)/d or work energy theorem?
 
  • #6
SammyS
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Okay that makes sense. thank you.

So if i were to calculate work done by friction, but this time I'm given distance and delta K, would I use Wncf=fd where f=(deltaK)/d or work energy theorem?
That gives you the friction (force) itself.
 

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