Soccer ball rebouncing of the goal post

[brundlfly]

Homework Statement

A 420 g soccer ball traveling at 23 m/s hits the goal post and rebounds at 18 m/s. If the ball is in contact with the post for 3.3 ms, what is the average acceleration of the ball during this time interval?

Homework Equations

Here I used 23m/s as initial velocity v_i and 18m/s as the final velocity v_f, and t = 0.0033s as the time traveled.

The Attempt at a Solution

I used a_x = v_f - v_i / t, so 18-23/0.0033 which gave me -1515.15m/s^2, which in my opinion seems to be a whole lot. Then I noticed that I can't use the goal post contact time as time traveled. So I am trying to find the time the ball actually traveled from start to hit the post and from rebound to the stop of the ball. Given those values I am stuck finding out how to get the time.

 

[Princu]

Ah..you made a mistake..a=change in velocity/time taken
the direction of ball changes after rebound so change in velocity=(18-(-23))
And acceleration=(40)/0.0033
and also don't worry about the magnitude of acceleration.The force acting on the soccer will be impulsive(have very large value) so the acceleration will also be very high