A roller-coaster car of mass 1700 kg is initially at the top of a rise at point a. It then moves 29.4 m at an angle of 50° below the horizontal to a lower point b. (a) Find both the potential energy of the system when the car is at points a and b and the change in potential energy as the car moves from point a to point b , assuming y = 0 at point b.(b) Repeat part (a), this time choosing y = 0 at point c, which is another 15.0 m down the same slope from point b.