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Homework Help: Speed of rocks when they hit the ground

  1. Jun 9, 2013 #1
    1. The problem statement, all variables and given/known data

    If I throw a rock upwards with an initial velocity and throw a rock downwards, what is the speed of the rocks just before they hit the ground?

    2. Relevant equations

    3. The attempt at a solution\

    They should hit the ground at the same speed and different times. I would use the conservation of mechanical energy, but someone I'm speaking to disagrees with me that they have same speed.

    How would you show this mathematically?
  2. jcsd
  3. Jun 9, 2013 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Use the formulas for objects traveling in a gravity field. You are studying physics, I presume.
  4. Jun 9, 2013 #3
    See your initial kinetic energy is the final potential energy.
    use this relation.
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