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Homework Help: Bouncing Ball Graph/Quadratic Formula

  1. Sep 2, 2011 #1
    1. The problem statement, all variables and given/known data
    The graph I have posted is the result of using a motion sensor above a bouncing ball.
    I am asked to write a clear interpretation of the meaning of each parameter in the equation Y=At^2+Bt+C.


    2. Relevant equations
    Y=Ax^2+Bt+C
    y=y0+v0t+1/2at^2


    3. The attempt at a solution
    http://imageshack.us/photo/my-images/687/screenshot20110902at112.png/
    I think relating the above two equations that B is the initial velocity and C is the initial position. "A" however is confusing me.
    Also if C is indeed the initial position I'm not quite sure I understand why it is negative.
     
  2. jcsd
  3. Sep 3, 2011 #2

    ehild

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    X in the first equation should be t. So how is A related to the parameter a ?

    The ball moves under the effect of gravity - what is the value of a?

    ehild
     
  4. Sep 3, 2011 #3
    sorry didn't see that typo!

    a would just be the gravitational acceleration correct? So -9.80 m/s^2?
    I'm still confused as to how they relate though. Does that mean A is half that of the gravitational acceleration?
     
  5. Sep 3, 2011 #4

    ehild

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    Yes.

    ehild
     
  6. Sep 3, 2011 #5
    Alright thank you!
    I'm just confused as to why it changes (shown on that graph)?
     
  7. Sep 3, 2011 #6

    ehild

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    The parabola is upside-down, so the A parameter is negative (like the gravitational acceleration, which points downward) A=-9.8/2.

    ehild
     
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