need help with 2 probelms - 1 "simple" one 1) a 50.0 g superball traveling at 25.0 m/s bounces off a brick wall and rebounds at 22.0 m/s. a high-speed camera records this event. if the ball is in contact with the wall for 3.50 ms, what is the magnitude of the average acceleration of the ball during this time interval? (note: 1ms = 10^-3s) heres how I tried to do this problem. first, I converted 3.50 ms to seconds which is .0035 seconds. Im assuming this will be my change in time. now, avg acceleration = change in velocity / change in time so heres how i tried to get change in velocity. since the final velocity of the ball right before it hit the wall is -25 m/s (Vf1) [negative because its going towards the wall] , that would then become the Initial velocity when it bounces off the wall(Vi2).....and so Vf2 is +22.0 m/s. [positive since its going away from the wall]. is my logic here right? avg accel = +22 - (-25)/.0035 = 13428.57m/s^2!!!!!! does that not seem right at all!!! 2) a 745i BMW car can brake to a stop in a distance of 121 ft. from a speed of 60 mi/h. to brake to a stop from a speed of 80 mi/h requires a stopping distance of 211 ft. what is the average braking acceleration for a) 60mi/h to rest b) 80 mi/h to rest c) 80 mi/h to 60 mi/h. when they say average braking acceleration.....do they mean "average acceleration" like the problem above? I figure its something more complicated than that, can someone point me in the right direction for this?