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My Physics homework regarding energy/velocity?

  1. Feb 13, 2012 #1
    1. The problem statement, all variables and given/known data

    [If a ball of mass (400g) falls from a height of (1.5m) towards the ground, and rebounds a height of (1m), find:

    a) Initial Potential Energy
    b) Kinetic Energy of ball before hitting the ground
    c) Velocity at which it reaches the ground
    d) The velocity at which it leaves the ground
    e) Initial Kinetic Energy
    f) Energy lost to it's surroundings]

    2. Relevant equations

    GPE = mgh
    KE = 1/2mv^2 (I think this is relevant..)

    and I don't know what else, that's the problem..

    3. The attempt at a solution

    a) = mgh = .4x10x1.5 = 6J?
    b) Final KE = Initial GPE (I think...), so = 6J?
    c) v = square root of 37?
    d) no idea where to even start..
    e) I think this is 0, because it doesn't move initially?
    f) no idea where to start...

    Anyone able to provide me some insight? Thanks.
  2. jcsd
  3. Feb 13, 2012 #2


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    Right. It's not moving initially, so all of its energy is potential.
    Right. Energy is conserved during the fall, so the initial potential energy is equal to the final kinetic energy.
    Not sure where this came from. Show us your calculations.
    You need to work this part the same way you did the first part, but this time you know the final potential energy. For part (e), you're supposed to find the speed the ball is moving as it starts its upward trajectory.
    After the bounce, it doesn't reach the same height it started at, so what does that tell you about the ball's energy?
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