800 kg roller coaster is initially at the top of a rise, at point A. It then moves 125 ft (38.1 m), at an angle of 40.0° below the horizontal, to a lower point, B. (a) Choose point B to be the zero level for gravitational potential energy. Find the potential energy of the roller coaster-Earth system at points A and B and the change in potential energy as the coaster moves. To start, I aimed to find the potential energy at point A: Ug = mgh Ug = (800)(9.8)(y component of h) Ug = (800)(9.8)(38.1sin40) Ug = 222561.92 J What am I missing in my process? Thanks in advance.