A 1500-kg roller coaster train is initially at the top of a rise, at point A. It then moves 140 ft, at an angle of 50. 0°below the horizontal, to a lower point B. Choose point B to be the zero level for gravitational potential energy. Find the potential energy of the roller coaster-Eqrth system at points A and B, and the change in potential energy as the coaster maves.