Well if you think about it, most of a rollercoaster's power is generated through gravity. A lot of the energy needed to run something like the Behemoth or Top Gun is going into the lift hill, and the occasional brake station, but other than that it's all the work of gravity.
I don't take physics, so I really have no idea what I'm talking about, just winging it, but hmm something like the distance/slope needed to on a downhill to make sure the train has enough velocity to get up the uphill? Maybe touch on something like how the car would be affected if there was nobody in it, versus a full train.
Maybe if you had stayed at Hillfield................ :)