posted by Anonymous .
A 1 x10^3 kg roller coaster car is initially at the top of a rise, at point A. It then moves 50 m at an angle of 40 degrees below the horizontal to a lower point, B. (a) Choosing point B as the zero level of gravitational potential energy, find the potential energy of the car at A and B, and the difference in potential energy between these points. (b) Repeat part (a), choosing point A as the zero reference level.