# Soccer ball rebouncing of the goal post

1. Oct 6, 2013

### brundlfly

1. The problem statement, all variables and given/known data
A 420 g soccer ball travelling 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?
2. Relevant 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.
3. 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.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Oct 6, 2013

### 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