A 50.0 g Super Ball traveling at 27.0 m/s bounces off a brick wall and rebounds at 15.0 m/s. A high-speed camera records this event. If the ball is in contact with the wall for 4.50 ms, what is the magnitude of the average acceleration of the ball during this time interval? I can't seem to get this problem right. Initially i converted 4.5ms to .0045s. Then I chose a time such as 4s to determine a distance and have a time perspective. I then multiplied 27x4 to determine the distance and got 108m, Then I determined the time it would take for the ball to return and got 7.2s. Then I used all this info with the .0045 included in the total time to calculate the average acceleration= (vf-vi)/(tf-ti). when everything was plugged in, (15-27)/(11.2045-0)=1.071m/s^2(assuming the absolute value is what they want when they say magnitude) This is wrong. Any help will do thanks.