physics
posted by Tamera .
A tennis ball with a speed of 6.0 m/s is thrown perpendicularly at a wall. After striking the wall, the ball rebounds in the opposite direction with a speed of 4.0 m/s. If the ball is in contact with the wall for 0.012 s, what is the average acceleration of the ball while it is in contact with the wall? Take the initial direction of motion to be the positive direction. (Indicate the direction of the acceleration by the sign of your answer.)

Initial velocity is given, final velocity is given, and the time is given. Using these, rearrange
v=u+at to solve for a.
The ball is slower after the bounce, so what sign will the acceleration be?