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Homework Help: Bouncing Ball Momentum

  1. Oct 8, 2011 #1
    1. The problem statement, all variables and given/known data
    I am currently working on a lab that deals with a bouncing ball where I need to find the KE and impulse yet I have no mass given.

    2. Relevant equations

    3. The attempt at a solution
    I have calculated KE by first finding the PE in the middle of the bounce where they will be equal.
    So half way from the highest point I calculated PE using PE=mgh. Then assumed KE was the exact same.

    I am however confused as to how to calculate impulse since I have no mass, just a KE value.
  2. jcsd
  3. Oct 8, 2011 #2
    well what ARE you given?
  4. Oct 8, 2011 #3
    The height of the first bounce was 0.799 m. Therefore half that distance is 0.3995 (Where KE and PE are equal). I then took this is used it in the PE equation. The mass of the ball is not changing however so I don't see that it's needed.
    Therefore PE=mgh
    PE=0.3995m x 9.8
    Therefore KE=3.92.

    I don't know how to get impulse from this.
  5. Oct 8, 2011 #4
    Ep isn't 3.92

    if you take Ep=Ek at halfway point then:


    therefore it is implied that


    but it is not implied that Ep=gh....

    I don't see what impulse you're looking for? If it's the impulse the ball has when it hits the ground it depends on how squishy the ball is.
  6. Oct 8, 2011 #5
    If all you've been given is the height of the first bounce the question is not answerable.
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