Hobbes sleds down a snowy hill that is frictionless, as shown. His inflatable sled, which has a total mass M with Hobbes on it, travels down to the bottom and is moving at a speed of 3.5v0 when it collides with Calvin's inflatable sled, which has a total mass (including Calvin) of 1.5M. Calvin's sled is at rest at the bottom of the hill before the collision, and immediately afterwards it moves to the right with a speed of 2v0. Express your answers to the following questions in terms of M, v0, and fundamental constants. (a) What is the height h of the hill that Hobbes slid down?

(b) What is the speed of Hobbes's sled after the collision?

(c) Calvin's sled slides a distance D before coming to a stop. What is the coefficient of kinetic friction between the ground and Calvin's sled?

(d) Is the collision between the two sleds elastic or inelastic? Justify your answer.