1. Two railroad cars, each of mass 7650kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision? Here does the thermal energy mean like to find friction? I used the conservation of energy formula, but it didn't work out. I don't really know what thermal energy is. 2. A ski starts from rest and slides down a 22 degrees incline 75 m long. If the snow is level at the foot of the incline and has coefficient of friction 0.09, how far will the ski travel along the level? Then, i think i also need to use conservation of energy, find out velocity, then find distance? Hope you can give me some hint, thank you.