AP Physics, I'm struggling.?

Question

A 42 g superball traveling at 21.5 m/s bounces off a brick wall and rebounds at 18.0 m/s. A high-speed camera records this event. If the ball is in contact with the wall for 3.05 ms, what is the magnitude of the average acceleration of the ball during this time interval? (Note: 1 ms = 10-3 s.)

Answer 1

u = impinging velocity = - 21.5 m/s

v = rebound at 180 deg backwards = + 18 m/s

change in momentum = mv - [- mu] = m[18+21.5] = 39.5 m

impulse = F (average force) * delta t = change in momentum

F (average force) = 39.5 m/3.05*10^-3

average acceleration = F/m = 39.5 /3.05*10^-3 = 12950.82 m/s^2