Sorry I'm late. Also sorry you couldn't handle any of this on your own.
There's not that much to it. If you ignore friction, then the total energy
is constant.
-- At the top, it's all potential energy, and kinetic energy is zero.
-- At the bottom, potential energy is zero and it's all kinetic energy.
-- Halfway down, it's half potential energy and half kinetic energy.
The real truth is that there's always some friction, friction robs kinetic
energy whenever he's moving, so eventually he stops going up and
down. Then he has to put some muscle energy into it to go some more.
