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Homework Help: Initial Velocity (Without time and acceleration)

  1. Sep 16, 2009 #1
    1. The problem statement, all variables and given/known data
    You are standing at the top of a cliff that has a stair step configuration. There is a vertical drop of 7 m at your feet, then a horizontal shelf of 9 m, then another drop of 3 m to the bottom of the canyon, which has a horizontal floor. You kick a 0.26 kg rock, giving it an initial horizontal velocity that barely clears the shelf below.

    What initial horizontal velocity v will be required to barely clear the edge of the shelf
    below you? How far from the bottom of the second cliff with the rock land?

    2. Relevant equations


    3. The attempt at a solution
    Cant seem to get around the problem without knowing more.
    Last edited: Sep 16, 2009
  2. jcsd
  3. Sep 16, 2009 #2


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    Can you find the time required for the rock to reach the point where it barely clears the edge of the shelf?
    Last edited: Sep 16, 2009
  4. Sep 16, 2009 #3
    I havent been able to
  5. Sep 16, 2009 #4
    You can find the time by using gravity and the fact that the first step is 7 meters down. How long does it take for the rock to fall 7 m? If you find it you can calculate how fast it must travel in a horizontal direction.
  6. Sep 16, 2009 #5
    Could you help me out a little more?
  7. Sep 16, 2009 #6
    So im assuming you mean:
    7m/9.8=.7142857s to make it to the bottom =t



    that not right?
  8. Sep 16, 2009 #7
  9. Sep 16, 2009 #8


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    Use the equation that you initially quoted as "relevant" for the vertical motion. Identify ll the quantities - you know all of them except the time. Remember, vertical motion only.
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