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Trajectory, does it clear a certain height problem help!

  1. Jun 3, 2009 #1
    Trajectory, "does it clear a certain height" problem help!

    1. The problem statement, all variables and given/known data
    A place kicker must kick a football from a point 45.5 m from the goal, and the ball must clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 19.0 m/s at an angle of 48.0° to the horizontal. By how much does the ball clear or fall short of clearing the crossbar?


    2. Relevant equations
    Dy = distance in y = Voy *t -1/2gt^2
    Dx = ~~~ x = Vox * t
    Vox = initial velocity in x
    Voy = ~~~~ y

    3. The attempt at a solution
    I tried to express Y in terms of x...
    since x = Vox * t .... t = x / Vox
    then
    Dy = Voy(x) / Vox - 4.9 (x^2/Vox^2) assume gravity's 9.8

    Plug in 45.5 m for x
    Voy = 14.12 m/s
    Vox = 12.71 m/s

    Dy = -12.23 m

    So when the ball is 45.5 m long, its 12.23m underground. which means the ball is 12.23 - 3.05 = 9.18m short of crossing the bar.

    Idk... seems simple enough but apprently the answer's wrong.

    Thanks alot for your help!
     
  2. jcsd
  3. Jun 3, 2009 #2

    rl.bhat

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    Re: Trajectory, "does it clear a certain height" problem help!

    With a speed of 19.0 m/s at an angle of 48.0° to the horizontal, find the range.
     
  4. Jun 3, 2009 #3
    Re: Trajectory, "does it clear a certain height" problem help!

    Ahhhhhhh i figured it out... since its "underground"... you add the 3.05 meters!
    thanks for the helps anyways >.<
     
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