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Homework Help: Horizontal Projectile Motion

  1. Oct 2, 2013 #1
    1. The problem statement, all variables and given/known data

    A ball is thrown horizontally from the top of a building and lands 20.0m away from it. If the ball is initially thrown at a velocity of 10.0m/s, how high is the building? How long does it take for the ball to reach the ground?

    2. Relevant equations

    dv = Viv * t + 1/2a * t

    3. The attempt at a solution

    dh (horiz.distance) = 20.0m
    Vh = 10.0m/s
    Viv (vertical init. velocity) = 0m/s
    a = -9.8m/s
    dv (vert. distance) = ?
    t = ?

    I'm confused because I'm missing two of the variables which are needed in the equation that will solve this problem...? (dv and t)
  2. jcsd
  3. Oct 2, 2013 #2


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    Staff: Mentor

    The horizontal velocity of the ball is fixed and constant during the whole time of flight. Knowing this, you can determine the time of flight.
  4. Oct 3, 2013 #3
    Using the same equation as the one stated above? Because that one's giving me a totally wrong answer.
  5. Oct 3, 2013 #4


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    Science Advisor
    Homework Helper
    Gold Member

    Yes, the same equation, but of course in the horizontal direction a = 0. pls post your working.
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