A red billiard ball moving at 4 m/s hits a green one of equal mass which is at rest. If the collision is perfectly elastic, what are the speeds of the red and the green ball after the collision ?

Complete these sentences. if a roller coaster train has a potential energy of 1,500 j and a kinetic energy of 500 j as it starts to travel downhill, its total energy isj. once the roller coaster train gets closer to the bottom of the hill, its kinetic energy increases to 1,100 j, and its potential energy decreases to j. when the train reaches the bottom of the track and is traveling along the ground, its kinetic energy isj.