A 30 kg child starts at rest at the top of a water slide that is 4 meters above the surface of the water. a) Calculate the gravitational potential energy of the child when they are at the top of the slide. b) Calculate the speed of the child when they are 2 meters above the water. c) If the child is moving at 7 m/s when they reach the surface of the water, how much mechanical energy was transformed into nonmechanical energy (heat and sound)?