Calculate the work done by friction

[cc2hende]

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

 

[SammyS]

Welcome to PH.

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

Hint: What does the Work-Energy Theorem say?

 

[cc2hende]

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?

 

[SammyS]

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.

 

[cc2hende]

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?

 

[SammyS]

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.