A roller coaster with a mass of 800 kg sits stationary at the top of a section of track, 75 m above the ground as shown. When the brake is released, it starts to roll down the track. For each height indicated in the diagram, calculate the gravitational potential energy and record in the table. Assuming that there is no friction, determine the mechanical kinetic energy and calculate the velocity for each of the heights of the rollercoaster and record in the table. height is 75m, 60m, 45m, 30m,15m.