At the top of the hill of a roller coaster, the cars have 10,000 joules of gravitational potential energy (GPE). Before the roller coaster begins to move, how much total energy is in the system?
a) 0 joules because the ride has not started.
b) 10,000 joules because the amount of GPE at the top of the hill is the total energy in the system.
c) 5,000 joules because the potential energy is divided equally.
d) 20,000 joules because the energy doubles at the top.