What are the energy transformations that occur as you coast down a long hill on a bicycle and apply the brakes?
Alternately, perhaps during your ride down the hill you allow one or more cycles of this sequence. You may allow velocity to increase to some limit and then clamp down on the brakes (until reaching a safer speed). In that case, this is a more accurate description of energy transformations:
Gravitational potential energy is converted into an increase in kinetic energy which is then converted to work done by the brakes where it escapes as heat.
I hope this helps,