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Math Help - projective fired

  1. #1
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    projective fired

    a projectile is fired from a cliff 100m high with a velocity of 200m/s. If the angle of projection is 20degrees above the horizontal, find the time of flight correct to 2 decimal places and the range of the projectile from the base of the cliff to the nearest metre. (assume g=9.8 metres per second per second)

    Can someone please give me the answers to this question. Explanation is not nessecary. i just need to verify my answers. thanx
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  2. #2
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    Quote Originally Posted by chrisgo View Post
    a projectile is fired from a cliff 100m high with a velocity of 200m/s. If the angle of projection is 20degrees above the horizontal, find the time of flight correct to 2 decimal places and the range of the projectile from the base of the cliff to the nearest metre. (assume g=9.8 metres per second per second)

    Can someone please give me the answers to this question. Explanation is not nessecary. i just need to verify my answers. thanx
    S_y = u_yt - \frac12 gt^2
    -100 = (200\sin 20^{\circ})t - \frac12 g t^2
    \implies t=15.29, \ -1.33
    Time cannot be negative hence t= 15.29s

    S_x = u_xt
    S_x = (200 \cos 20^{\circ})(15.29) = 2874m


    EDIT: Drawing a diagram for these type of question does help.
    Attached Thumbnails Attached Thumbnails projective fired-projectile.jpg  
    Last edited by Simplicity; July 11th 2008 at 04:16 AM. Reason: Diagram
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by Air View Post
    S_y = u_yt - \frac12 gt^2
    -100 = (200\sin 20^{\circ})t - \frac12 g t^2
    \implies t=15.29, \ -1.33
    Time cannot be negative hence t= 15.29s

    S_x = u_xt
    S_x = (200 \cos 20^{\circ})(15.29) = 2874m


    EDIT: Drawing a diagram for these type of question does help.
    You have answered this now, but the correct response would have been to ask the original poster what their answer was, then a simple yes or no would suffice.

    That way we minimise the possibility of giving the answer needed for a multiple choice question where the poster is not interested in learning how to solve the problem.

    Also if they are honest they already know the solution method so you are wasting effort typing the thing out.

    Also, check your calculations, you seem to have lost precision somewhere, so your answer is not correct to the nearest metre.

    RonL
    Last edited by CaptainBlack; July 12th 2008 at 01:14 AM.
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