## College Physics (4th Edition)

We can rank the points in order of mechanical energy, from greatest to least: $A \gt B \gt C \gt D \gt E$
By conservation of energy, the mechanical energy would be constant for all points in the motion if the external work was zero. However, because of friction and air resistance, the external work is non-zero. During the motion, the forces of friction and air resistance do negative work on the skier, thus removing mechanical energy from the skier. Therefore, the skier's mechanical energy decreases throughout the motion. The skier's mechanical energy is a maximum at the start and a minimum at the end of the motion. We can rank the points in order of mechanical energy, from greatest to least: $A \gt B \gt C \gt D \gt E$