What part of the roller coaster has kinetic energy?

Mechanical Energy encompasses both Kinetic and Potential energies. A roller coaster is a perfect example of both. At the very top of a hill, the roller coaster has a lot of potential energy due to position above the earth. As it goes down a hill, this potential energy decreases as it gets closer to the earth, and it's kinetic energy increases as it gets faster.

KE = energy of motion

PE = potential energy due to position above the earth

ME = KE+PE