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Homework Help: Throwing a dart from a roof - Velocity

  1. May 8, 2010 #1
    1. The problem statement, all variables and given/known data

    A dart is thrown horizontally from a buildings rooftop. The dart's time of flight is 2.0 s. The dart sticks in the ground such that it makes a 53.1 degree angle with the ground.

    With what speed was the dart thrown?

    3. The attempt at a solution

    I am studying for my final and i do not get this problem from one of my previous tests.

    The answer is 14.7 m/s and i have no idea how to get it. Can anyone point me in the right direction.

    Thank you :)
  2. jcsd
  3. May 8, 2010 #2


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    Homework Helper

    Well if it is throw horizontally, then the initial vertical velocity is zero right? Using an equation of motion, what would be final vertical velocity when t=2?
  4. May 8, 2010 #3
    Is the final vertical velocity when t=2 just 19.6 m/s

    I got that from

    Vf = Vi + at

    oh so then from that the x component of the Vf will be the same as the velocity initial correct?


    tan(53.1) = 19.6 / Vfx

    Vfx = 14.7 m/s

    Does that seem right?
  5. May 8, 2010 #4


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    Homework Helper

    Yes that looks correct.
  6. May 8, 2010 #5
    Yay! thank you very much :)
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