A roller coaster car starts from rest at the top of a tall hill and rolls down to the bottom. The car then travels along a flat section of track before coming to a stop. Explain the energy transfers that take place from the moment the car begins to move until it comes to a stop on the flat section. In your answer, refer to useful energy transfers, waste energy transfers, and the conservation of energy.

The car starts from rest at the top of the hill, so its initial energy is all gravitational potential energy (GPE). As it rolls down, the GPE decreases and is converted into kinetic energy (KE) – this is a useful energy transfer. During the descent some of the energy is lost as thermal energy (heat) in the wheels, brakes and air resistance; this is a waste energy transfer. When the car reaches the flat section it has a large amount of KE. While travelling on the flat, friction between the wheels and the track and air resistance convert the KE into thermal energy and a small amount of sound energy – another waste energy transfer. The car slows down until all its KE has been dissipated as heat and sound, and it comes to a stop. Throughout the whole motion the total energy of the system is conserved – energy is neither created nor destroyed, only transferred or dissipated.