Step-by-step explanation:
Before the roller coaster starts moving, it is at rest and energy at rest is potential energy. As the roller coaster moves the potential energy is converted to kinetic energy as kinetic energy is energy in motion. As it gets to the top of a hill it assumes a rest position from a height for a short time and as it comes down the potential energy is converted again to kinetic energy. This continues for the whole ride until it comes to an end.