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Homework Help: Using GPE and KE to find speed

  1. Jan 14, 2009 #1
    1. The problem statement, all variables and given/known data
    After falling 5m a rock has a velocity of v. What is the total distance the rock must fall to get a speed of 2v?


    2. Relevant equations
    GPE=mgh
    Ke=1/2mv^2
    3. The attempt at a solution
    Should I set both equations equal to each other? I'm not even sure how to begin this one.
     
  2. jcsd
  3. Jan 14, 2009 #2

    LowlyPion

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    Homework Helper

    You can do it that way. Note that v = (2*g*h)½

    If v ∝ h½ ...

    ... how much then do you need to increase the height to get a doubling of speed?
     
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