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Solving initial velocity for falling object

  1. Feb 12, 2015 #1
    1. The problem statement, all variables and given/known data
    A stone is dropped from a bridge that is 65 m high. A second stone is thrown downwards 2 seconds later. Both the stones are heard hitting the water at the same time. The speed of sound is a constant 343 m/s. What is the initial velocity of the second stone.

    2. Relevant equations
    d=vi*t+1/2at^2

    3. The attempt at a solution
    65=0+1/2(-9.8)(t)^2

    I know t-2 is used for the time of the second stone. I don't know which equations to use to make them equal.
     
  2. jcsd
  3. Feb 12, 2015 #2

    gneill

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    Your Relevant equation should suffice.

    What value did you get for the time of fall for the first stone? So what must be the time (numeric value) that the second stone has to make the complete journey?
     
  4. Feb 12, 2015 #3
    5.2. Do I just sub it in to the second equation with t-2 and solve for initial velocity?
     
  5. Feb 12, 2015 #4

    haruspex

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    Sure.
     
  6. Feb 12, 2015 #5
    So the speed of sound is irrelevant?
     
  7. Feb 12, 2015 #6

    haruspex

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    The sounds of hitting the water were heard at the same time. Did they hit the water at the same time?
     
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