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Math Help - Projectile Cruves problem

  1. #1
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    Projectile Cruves problem

    Hi
    The following question i am having problem with:
    A tennis ball is served horizontally from 2.5m above the ground at 30m/sec. The net is 12m away and 0.9m high.
    a) Find its velocity (v) at any time t seconds

    This is what i done:

    a=-gj

    find the integral to get velocity

    v=c_1 i + (-gt+c_2)j

    v=12.6i+(-9.8t+2.5)j

    P.S
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  2. #2
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    the position and height of the net have nothing to do with the ball's velocity unless the ball hits it.

    v(t) = 30i - (gt)j

    0 \le t < \sqrt{\frac{5}{g}}
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  3. #3
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    Hello, Paymemoney!

    A tennis ball is served horizontally from 2.5 m above the ground at 30 m/sec.

    a) Find its velocity (v) at any time t seconds.

    This is a Projectile problem; there is vertical and horizontal displacement.

    The horizontal position is: . x \:=\:30t

    The vertical position is: . y \:=\:2.5 - 4.9t^2


    The velocity is a vector; it has magnitude and direction.

    . . The magnitude is: . |\vec v| \;=\;\sqrt{\left(\frac{dx}{dt}\right)^2 + \left(\frac{dy}{dt}\right)^2}

    . . The direction is: . \theta \;=\;\tan^{-1}\left(\dfrac{\frac{dy}{dt}}{\frac{dx}{dt}}\right  )
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  4. #4
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    So the velocity would be 30-\sqrt{9.8t}
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  5. #5
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    Quote Originally Posted by Paymemoney View Post
    So the velocity would be 30-\sqrt{9.8t}
    no, it would not.
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