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Math Help - [SOLVED] Projectile Motion

  1. #1
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    Exclamation [SOLVED] Projectile Motion

    Hi

    Gee Ming the golfer hits a ball from level ground with an initial speed of 50m/s and an initial angle of elevation of 45 degrees. The ball rebounds off an advertising hoarding 75 m away. Take g = 10m/s^2

    a) Show that the ball hits the hoarding after 3/2 * sqrt(2) s at a pt 52.5 m high.

    b) Show that the speed v of the ball when it strikes the hoarding is 5 sqrt(58) m/s at an angle of elevation alpha to the horizontal, where alpha = arctan (2/5).

    c) Assuming that the ball rebounds off the hoarding at an angle of elevation alpha witha speed of 20% of v, find how far from Gee ming the ball lands.

    How exactly do i do c???

    By the way, the answer's meant to be 50 m
    Last edited by mr fantastic; May 21st 2010 at 02:41 PM. Reason: Merged posts.
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  2. #2
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    Quote Originally Posted by UltraGirl View Post
    Hi

    Gee Ming the golfer hits a ball from level ground with an initial speed of 50m/s and an initial angle of elevation of 45 degrees. The ball rebounds off an advertising hoarding 75 m away. Take g = 10m/s^2

    a) Show that the ball hits the hoarding after 3/2 * sqrt(2) s at a pt 52.5 m high.

    b) Show that the speed v of the ball when it strikes the hoarding is 5 sqrt(58) m/s at an angle of elevation alpha to the horizontal, where alpha = arctan (2/5).

    c) Assuming that the ball rebounds off the hoarding at an angle of elevation alpha witha speed of 20% of v, find how far from Gee ming the ball lands.

    How exactly do i do c???

    By the way, the answer's meant to be 50 m

    For part a, v_o=50m/s at 45^o therefore,

    v_{o_x}=25m/s and v_{o_y}=25m/s

    v_{o_x} is constant so the time it takes the ball to travel to the sign should be given by the equation,

     time=\frac{distance}{velocity}=\frac{75m}{25\frac{  m}{s}}=3s

    which is pretty close to \frac{3\sqrt{2}}{2}

    am I missing something here?
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  3. #3
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    Exclamation

    Sorry for the inconvenience but I've done both a + b. I just dont know how to do c.
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  4. #4
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    yay. managed to solve it myself.
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