A sled and rider with a combined mass of 70 kg are at the top of a hill that rises 9 m above the level ground below. The sled is given a push, providing an initial kinetic energy at the top of the hill of 1,200 J. a. Choosing a reference level at the bottom of the hill, what is the potential energy of the sled and rider at the top of the hill? sled and rider at the top of the hill? of the sled and rider at the bottom of the hill? b. After the push, what is the total mechanical energy of the hill?c. If friction can be ignored, what will be the kinetic energy of the sled and rider at the bottom of the hill?