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Homework Help: Catapult gravity problem

  1. Jan 3, 2012 #1
    1. The problem statement, all variables and given/known data

    A knight sits on a castle wall during a siege.
    To while away the time, he notes that boulders catapulted from below land on the top of
    his wall with a vertical velocity of 9.2 m/s.
    If he is 40 m above the catapult, what
    is the initial velocity of the boulders? The
    acceleration of gravity is 9.8 m/s^2

    Answer in units of m/s

    2. Relevant equations
    Δd=v^2f-v^2i-2a

    3. The attempt at a solution
    -10.4
     
  2. jcsd
  3. Jan 3, 2012 #2

    SammyS

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    What equation is that ?

    vf2 = vi2 -2g(Δd)
     
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