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!