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Homework Help: Velocity of a falling rock

  1. Sep 7, 2009 #1
    1. The problem statement, all variables and given/known data
    b) A person standing on the edge of a 100 m high cliff drops a 0.5 kg stone vertically downwards. Determine the final velocity of the stone after falling 100m, and its kinetic energy.

    2. Relevant equations
    Final velocity
    v = √(2gx)

    3. The attempt at a solution

    final velocity

    v = √(2gx)
    v = √(2(0.5x9.8)100)
    v= 31.3m/s
    is that correct?

    how do i calculate the kinetic energy?
  2. jcsd
  3. Sep 8, 2009 #2
    Are you familiar with conservation of energy or the kinetic energy formula?
    Last edited: Sep 8, 2009
  4. Sep 8, 2009 #3


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    The velocity is wrong. You don't use the mass to calculate it (see your formula).
    The mass is used to calculate the kinetic energy.
  5. Sep 8, 2009 #4
    so it will be

    v = √(2gx)
    v = √(2(9.8)100)
    v= 44.27m/s ?

    and no i dont know how to calculate the second part
  6. Sep 8, 2009 #5


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    Read the page of Wikepedia about kinetic energy
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