11.As you ascend the hill, your muscles are doing work, converting chemical energy from your food into a gravitational potential energy increase, as well as kinetic energy due to your motion. There is some friction present, so some of the kinetic energy is being converted to heat in the axles and tires of the bicycle. As you coast back down the hill, gravitational potential energy is converted to kinetic energy. The application of the brakes dissipates all of this energy as heat. Energy by itself does not refer to time.
Power is the rate of energy use or production.
It is an amount of energy divided by the time elapsed. So, one way of summarizing the relationship is to say that energy is equal to power multiplied by time. When your hair is wet, evaporation of the water in your hair is taking place. This evaporation of the water absorbs latent heat from the surroundings, which in this case is your head. This loss of heat makes your head feel cooler.