In order for a roller coaster to work, why does the hill the cart climbs need to be higher than the top of the loop?

The concept of potential energy, often referred to as energy of position, is very simple: As the coaster gets higher in the air, gravity can pull it down a greater distance. ... The potential energy you build going up the hill can be released as kinetic energy — the energy of motion that takes you down the hill.

a roller coaster works using gravity. the initial hill has to be high enough that gravity is able to produce enough momentum to complete the course.

car stops. he keeps going = he has inertia

increases it