Magnitude of Average Acceleration

AI Thread Summary
To find the magnitude of average acceleration of a Super Ball rebounding off a wall, the initial velocity is 27.0 m/s, and the final velocity is -15.0 m/s (negative due to direction change). The contact time with the wall is 4.50 ms, which is converted to 0.0045 seconds. Using the formula for average acceleration, a = (vf - vi) / t, the calculation yields a value of -9333.33 m/s², which is approximately 9333.33 m/s² when considering magnitude. The discussion highlights the importance of correctly applying the formula and understanding the direction of velocity changes.
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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.
 
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