52 Roger's tennis ball has a mass of 0.3 kg. If he holds the ball above the ground at a height of 2.0 m to serve, what is its potential energy? 53. Determine the kinetic energy of a 625-kg roller coaster car that is moving with a velocity of 18.3 m/'s. 54. A boy of 450 N of weight climbs a wood steps with a length of 3 m. The boy takes 6 seconds to get the end of the steps. What is the power done by the boy on this activity