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Homework Help: Kinematic Question maybe?

  1. Sep 11, 2008 #1
    1. The problem statement, all variables and given/known data
    A 50.0 g Super Ball traveling at 28.0 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 3.50 ms, what is the magnitude of the average acceleration of the ball during this time interval? (Note: 1 ms = 10-3 s.)

    2. Relevant equations
    i used Vxf = Vxi + at

    3. The attempt at a solution

    I put vxf = 19, vxi = 28 and t = 3.50 ms and .0035, i get an answer of - 2.57 and -2571 (respectively) and made it positive since its the magnitude, but its wrong. Any ideas?
  2. jcsd
  3. Sep 11, 2008 #2
    You must account for the fact that the ball changes direction, and so the velocities before and after have different directions.
  4. Sep 18, 2008 #3
  5. Oct 26, 2010 #4
    Impulse = F * t = change in momentum = (mv1 - (- mv2)

    F = average force
    a = F/m

    = (v1 +v2)/t
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