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Math Help - Projectiles

  1. #1
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    Projectiles

    A ball is kicked from point A on a horizontal field with an initial speed of 24.5 m/s at an angle of 30 degrees above the horizontal. The ball first hits the ground again at point B.

    Calculate the time of flight of the ball


    Ok so i have worked out

    Vx = 24.5cos30 = 21.218
    Vy = 24.5sin30 - 9.8t = 12.25

    now i'm assuming i have to do something with these numbers but I have no idea :S
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  2. #2
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    Quote Originally Posted by djmccabie View Post
    A ball is kicked from point A on a horizontal field with an initial speed of 24.5 m/s at an angle of 30 degrees above the horizontal. The ball first hits the ground again at point B.

    Calculate the time of flight of the ball


    Ok so i have worked out

    Vx = 24.5cos30 = 21.218
    Vy = 24.5sin30 - 9.8t = 12.25

    now i'm assuming i have to do something with these numbers but I have no idea :S
    \Delta y = v_0 \sin{\theta} \cdot t - \frac{1}{2}gt^2

    the overall displacement in the y-direction is 0 ...

    0 = v_0 \sin{\theta} \cdot t - \frac{1}{2}gt^2

    0 = t\left(v_0 \sin{\theta} - \frac{1}{2}gt\right)

    v_0 \sin{\theta} - \frac{1}{2}gt = 0

    t = \frac{2v_0 \sin{\theta}}{g}
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  3. #3
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    Quote Originally Posted by skeeter View Post
    the overall displacement in the y-direction is 0 ...

    This is what I was looking for thankyou!
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