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Homework Help: Help Free Fall Problem

  1. Sep 5, 2004 #1
    Help!! Free Fall Problem

    A pellet gun is fired straight downward from the edge of a cliff that is 13 m above the ground. The pellet strikes the ground with a speed of 30 m/s. How far above the cliff edge would the pellet have gone had the pellet been fired straight upward?
  2. jcsd
  3. Sep 5, 2004 #2


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    What have you done so far?
  4. Sep 5, 2004 #3
    I started using the equation :

    y=-1/2 gt^2-30t+0
  5. Sep 5, 2004 #4
    are you assuming that 30 m/s is not the pellets terminal velocity?
  6. Sep 5, 2004 #5


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    Have you learned about energy conservation yet? If so then you can use it to find what the "muzzle velocity" is. Basically it says that [itex]\frac{1}{2}mv^2_{final} - mg \times 30 = \frac{1}{2}mv^2_{initial}[/itex], i.e. potential + kinetic energy is constant.
  7. Sep 5, 2004 #6
    yes, i'm assuming that 30m/s is not the pellets terminal velocity
  8. Sep 5, 2004 #7


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    Hmmm, that's not the right equation - did you understand the remarks Tide made about energy conservation?
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