What is the total mechanical energy of a 575 kg roller coaster that is at rest 50.0 m above the lowest point on the ride? The maximum possible speed of the roller coaster is 31.3 m/s. (do not include units in your answer)

Answer 1

If it is at rest 50 m high, the total is
m g h = 575 * 9.81 * 50 = 282,037 Joules

The speed does not matter because we counted the total while at rest.
However let's see ho much kinetic energy it has at the bottom
(1/2) m v^2 = .5*575*31.3^2 = 281,660 Joules
so to 3 significant figures no energy was lost to friction while accelerating down the rails.