An empty roller-coaster car of mass 200kg starts from rest at the top of a 30m high hill. The track is frictionless. After descending to the valley at ground level, the car climbs a second hill that is 12m high.
a. (i) Calculate the speed of the car at the lowest point of the valley.
b. (ii) Determine its speed at the top of the second hill.
c. (iii) Would the answers in parts (i) and (ii) change if passengers of total mass 300kg were sitting in the car? Give a brief reason.