A 2.5 ball and a 3.5 ball, each moving at 0.90 , undergo a head-on collision. The lighter ball rebounds opposite its initial direction, with speed 0.90. a) Find the post-collision velocity of the heavier ball. Assume the initial direction of the lighter ball as positive. b) How much mechanical energy was lost in this collision? Express your answer in J. c) How much mechanical energy was lost in this collision? Express your answer as a fraction of the system's initial mechanical energy.