1. The problem statement, all variables and given/known data During a rockslide, a 710 kg rock slides from rest down a hillside that is 500 m long and 300 m high. The coefficient of kinetic friction between the rock and the hill surface is 0.23. https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/57/57890-5a3321dd6b8a58eb42038e3fc5bbe5e1.jpg [Broken] (a) If the gravitational potential energy U of the rock-Earth system is set to zero at the bottom of the hill, what is the value of U just before the slide? (b) How much energy is transferred to thermal energy during the slide? (c) What is the kinetic energy of the rock as it reaches the bottom of the hill? 2. Relevant equations U=mgh N=mgcosθ Fƒ=μN Wƒ=Fƒdcosθ 3. The attempt at a solution a) Easy. Uο=(710)(9.8)(300)=2087400 J (Accepted as correct answer) b) θ=tan-1(300/500)=31° N=(710)(9.8)cos(31)=5964.2 N Fƒ=(.23)(5964.2)=1371.8 N Wƒ=(1371.8)(583.1)cos(180°)=-799896.6 J (This was not accepted as correct answer) (c) Uο+Kο=Uf+Kf+Wƒ 2087400+0=0+Kf+799896.6 Kf=1287503.4 J (Also not accepted as correct answer) Please let me know where I went wrong.