posted by Cheng .
A billiard ball strikes and rebounds from the cushion of a pool table perpendicularly. The mass of the ball is 0.38 kg. The ball approaches the cushion with a velocity of +2.10 m/s and rebounds with a velocity of -2.00 m/s. The ball remains in contact with the cushion for a time of 3.10 × 10-3 s. What is the average net force (magnitude and direction) exerted on the ball by the cushion?