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Homework Help: Tennis Ball rebounds

  1. Feb 28, 2009 #1
    1. The problem statement, all variables and given/known data
    A 60 tennis ball with an initial speed of 33 hits a wall and rebounds with the same speed. The figure (Intro 1 figure) shows the force of the wall on the ball during the collision. t=6
    http://session.masteringphysics.com/problemAsset/1070440/4/09.EX11.jpg

    What is the value of , the maximum value of the contact force during the collision?


    2. Relevant equations

    p=mv
    change in p = F *change in time
    F=ma

    3. The attempt at a solution

    I attempted and got Fmax = 1320
     
  2. jcsd
  3. Mar 1, 2009 #2

    LowlyPion

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    Not sure about your units, but I'll go with 60 g for a tennis ball and 33 m/s.

    So maybe check your units.

    Impulse is Δmv.

    But your force varies during the time. So you want to take the integral of the area under the F - t graph they provide. Each square is an Fmax * 1ms. When you figure the area, then you can calculate Fmax by dividing the Impulse you found by the ms factor from the area you found.
     
  4. Mar 1, 2009 #3
    The graph doesn't provide F values so for area i got ((6+2)*Fmax)/2
    For impulse I got .06*33 = 1.98 ....(60 g is right -> .06 kg)

    But, I don't know what you mean by dividing the impulse by the ms factor?
     
  5. Mar 1, 2009 #4

    LowlyPion

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    The impulse is change in momentum. That would be twice what you show.

    Having found the area under the Force function you have that as 4*Fmax in units of N-s right?

    So take the Impulse and divide by the time - 4ms to yield the value of your Fmax looks like to me.

    Didn't you say F*Δt = I = Δmv ?
     
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