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I am having trouble relating to impulse

  1. Dec 7, 2008 #1
    1. A super ball, made of rubblerlike plastic, is thrown against a hard smooth wall. The ball has a mass of 4.0g and strikes the wall from a perpendicular direction with a speed of 15.0 m/s. For simplicity, assume that the acceleration is constant while the ball is in contact with the wall. After touching the wall, the center of mass of the Super Ball moves .50 CM toward the wall and then moves the same distance away to the complete the bounce.
    What is the magnitude of the impulse delivered by the wall?
    What is the magnitude of the time average force?

    2. dMomentum= MV'-MV, Impulse=(MV'-MV)/dt



    3. Pretty lost here. I tried relating the movement of the center of mass to the dt and then treating dmomentum. So [(-15m/s)(0.004kg)-(15m/s)(0.004gk)]=-0.12 N.S then
    1.2N/S/(0.005m/15m/s)
     
    Last edited: Dec 7, 2008
  2. jcsd
  3. Dec 7, 2008 #2

    Doc Al

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    Staff: Mentor

    The mass is 0.004 kg, not 0.04.
    What's the average speed during the collision? Use that to find the total time of the collision.
     
  4. Dec 7, 2008 #3
    Well the conversion is a little embarrassing but where I am lost is finding the average speed over the collision.
     
  5. Dec 7, 2008 #4

    Doc Al

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    Staff: Mentor

    Assume the acceleration over each half of the collision is uniform. The initial speed is V0 and the final speed is 0. So what's the average speed?
     
  6. Dec 7, 2008 #5
    Thank you so much I used the kinematics dx=1/2(dv)t, and got it.
     
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