During a rockslide, a 340 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 0.24. (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? (d) What is its speed then? For letter a i found the gravitational potential energy using the formula Eg=mgy. This gave me 999600 J. I'm not sure how to find the thermal energy though, i thought that i could just multiply the gravitational energy by the coefficient of friction, but that didn't work.