(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A 2.1 x 10^3 kg car starts from rest at the top of a driveway that's sloped at an angle of 20.0 degrees with the horizontal. An avg. friction force of 4.0 x 10^3 impedes the cars motion so that the cars speed at the bottom of the driveway is 3.8m/s. What is the length of the driveway?

2. Relevant equations

Wnet = change in KE

KE=1/2mv^2

(so you can substitute it)

Wnet = Fdcos(angle)

3. The attempt at a solution

I'm racking my brain here! I don't know what I'm doing wrong...

Wnet = (Fnet)(d)(cos angle)

Wnet = change in KE

Wnet = (KE f) - (KE i)

Wnet = KEf - 0

Wnet = 1/2mvf^2

*****note mvf is mass(final velocity)^2*****

1/2mvf^2 = Fdcos(angle)

1/2(2.1 x 10^3)(14.44) = 4.0 x 10^3(cos 20) (d)

15,162 = 3758.77d

d=4.03 m

**The book's answer is 5.1 m

Now, I'm not sure how to handle the fact that friction is acting in the opposite direction that the work is being done, so i dont know how to account for that negative work, since the answer is not negative.

But other than that, i dont know how to get 5.1

Any help is appreciated!

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# Homework Help: Work-Kinetic Energy Theorum Problem

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