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Homework Help: Falling object of volleyball

  1. Jul 10, 2007 #1
    1. The problem statement, all variables and given/known data
    Jason hits a volleyball so that it moves with an initial velocity of 6.0 m/s straight upward. If the volleyball starts from 2.0 m above the floor, how long will it be in the air before it strikes the floor?

    2. Relevant equations
    y=-2.0m,Vi=+6.0 m/s a=-9.81m/s^2
    vf^2=vi^2+2ay. then just put the numbers in it.

    3. The attempt at a solution
    I don't understand why the displacement here is -2.0m? I don't think it can be used in solving the problem because 2.0m is not the distance that the ball traveled, but just 2.0m above the floor? What's the significance of it?
  2. jcsd
  3. Jul 10, 2007 #2


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    The displacement is -2.oo m because that's the distance it ended up at from the starting point. If you think about the displacement time curve, it's a parabola, so if you read across the graph for a displacement of -2.oom, you have two time values, one of them has to be rejected to give the right answer.
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