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Homework Help: Projectile Motion Ball off Cliff Help

  1. Jan 25, 2012 #1
    I missed a few days of class and have a quiz tomorrow so I'm not entirely sure where to start with this. The question is:

    A golfer hits a ball (m = 38 g) from a cliff top (h = 46 m) and times how long it takes to splash in the ocean (t = 7.0 s). The ball hits the water at a distance (x = 154 m) from the vertical cliff bottom. Find the ball's initial velocity and the angle of launch.

    I have y = 46 m, x = 154 m, t = 7.0 s

    I assume I have to use the two-dimensional kinematic equations, but I just can't seem to get anywhere towards finding the initial velocity.

    My first thought was

    x = v_0x * t

    v_0x = 154 / 7 = 22 m/s

    Then take

    y = (v_0y)t+1/2 gt^2 = 7(v_0y) - 240.34

    v_0y = 40.905

    And then square both of those and take the square root. But the answer I get doesn't agree with the instructors, so I'm lost.
  2. jcsd
  3. Jan 25, 2012 #2
    You did not use the cliff height in the second equation.
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