Hello, I'm starting to study physics, and I have a problem that I have puzzled me for long... here it is. any help appreciated. thanks in advanced. A tennis ball with a speed of 23.6 m/s is thrown perpendicularly at a wall. After strik- ing the wall, the ball rebounds in the opposite direction with a speed of 14.6 m/s. If the ball is in contact with the wall for 0.014 sec, what is the average acceleration of the ball while it is in contact with the wall?