At which point in its ride does a roller- coaster have the greatest amount of kinetic energy?
This question can't be answered definitely with the amount of information given.
The moment the roller-coaster has the greatest amount of kinetic energy is equal to the moment when the roller-coaster experiences the greatest velocity. Since the mass is a constant in this case, it can be ignored. Because I have no further information about the natur of acceleration of the roller-coaster the point of time can not be determinated.