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Homework Help: Help on inelastic problem

  1. Mar 31, 2004 #1

    How do i find change in kinetic energy?

    Here is the problem:
    The rubber ball is dropped 2m elastically off the floor, so its speed immediately after bouncing is the same as immediately b4.
    If the rubber ball has a mass of 0.015kg and its velocity is 6.26m/s, what is its change in kinetic energy from immediately b4 the collision to immediately after the collision? Breifly justify your answer.

    Do i use this equation, KE = 1/2mv^2?

  2. jcsd
  3. Mar 31, 2004 #2
    Yup. Change in kinetic energy is just the kinetic energy after minus the kinetic energy before.

    So KE = 1/2*mv^2, now if m is the same for both and v is the same for both...

  4. Mar 31, 2004 #3
    So is my answer, 0.29N?
  5. Mar 31, 2004 #4
    Hold on now!

    1/2(.015kg)(6.26m/s)^2 - 1/2(.015)(6.26m/s)^2 = ?

    Also, what units do you get? Here's a hint: it's not Newtons! It's kinetic energy, so its units will probably be energy.

  6. Mar 31, 2004 #5
    I got 0 joules.
  7. Mar 31, 2004 #6
    Yup. And this makes sense, too, since this collision is elastic. Elastic collisions are collisions in which energy is conserved, so energy before had better equal energy after (and their difference had better equal zero)!

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