A child on a sled ( m=47.0kg) slides down a long hill starting from a rest position at a point 10.0 m higher in elevation than his finishing point. a) what is the total mechanical energy present? b) Assuming that there's no friction and no external pushes, determine the child's speed at the bottom of the hill. c) The child's speed at the bottom of the hill is actually 5.0 m/s. Explain whether or not this defies the law of conversation of energy.