At the roller rink, two \(20-\mathrm{kg}\) girls accelerate toward each other until they are each moving at \(2.0 \mathrm{~m} / \mathrm{s}\) in the Earth reference frame. They then collide stomach-to-stomach, grab on to each other, and fall to the floor. Calculate the momentum of each girl before the collision and after the collision \((a)\) in the Earth reference frame and \((b)\) in the reference frame of a mother who started skating with one of the girls and then continued on after the collision without changing speed.

(c) The fathers decide the collision looks like fun and give it a try. Explain, in terms of energy, why they don't enjoy it nearly as much as their daughters do.