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Math Help - please check my answer - another projectile motion question

  1. #1
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    please check my answer - another projectile motion question

    HI ,

    Could you please help me to check my answer for the below question? Thanks

    A projectile is launch with an initial speed of 140feet per second from a 20 feet tall tower at an angle of pi/3 to the horizontal. Assume that the only force acting on the object is gravity.

    Find the maximum horizontal range.

    Solution:

    x=70t
    y=70sqrt(3)t -16t^2

    The projectile will reaches its maximum horizontal range when it hit the ground that is when y=0.
    y=70sqrt(3)t -16t^2=0
    so t=0 (ignored) or t= 35sqrt(3)/8

    x=70t =70 x 35sqrt(3)/8 = 530.44 ft

    So the maximum horizontal range is 530.44ft.

    Is my answer correct? The reason I asked that because my friend got a different answer. Her answer is 541.8feet.
    Last edited by Jenny20; February 14th 2007 at 01:37 PM.
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  2. #2
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    Hello, Jenny!

    Sorry, your friend is right.
    . . You forgot about the 20-foot tower . . .


    . . x .= .70t
    . . . . . . . . . . . . ._
    . . y .= .20 + 70√3t - 16tē

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