A 28 kg bear slides, from rest, 6 m down a lodgepole pine tree, moving with a speed of 5.9 m/s just before hitting the ground. (a) What change occurs in the gravitational potential energy of the bear-Earth system during the slide? (b) What is the kinetic energy of the bear just before hitting the ground? (c) What is the average frictional force that acts on the bear? To start off with i set up an energy bar chart and i know that it begins with gravitational energy and ends with kinetic energy. The kinetic energy is Ek=1/2mv^2 so thats the answer for b. I'm not sure how to find the frictional force on the bear though, and i think i need that before i can figure out the change in the gravitational energy. I think that the frictional force would equal the product of the kinetic friction coefficient and the normal force. But i keep coming up with the wrong answers so i'm not sure.