Magnitude of the average acceleration

[swan777]

A 49.0-g Super Ball traveling at 27.0 m/s bounces off a brick wall and rebounds at 19.0 m/s. A high-speed camera records this event. If the ball is in contact with the wall for 3.65 ms, what is the magnitude of the average acceleration of the ball during this time interval?


I converted 3.65 ms to 0.00365 s and I know I need to use (v2-v1/t2-t1) but everytime I try to figure this problem out I am getting lost and coming up with the wrong answer somehow.

 

[swan777]

nevermind I figured it out :)

 

[bumpkin]

what signs on the velocity terms?

http://en.wikipedia.org/wiki/Acceleration#Average_and_instantaneous_acceleration