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Trouble Setting Up Projectile Motion

  1. Sep 24, 2004 #1
    Problem: A football is kicked from 36.0 m away from goal post at an angle of 53.0 deg. above horizontal at a speed of 20.0 m/s. The crossbar is at a height of 3.05 m high. a.) By how far does the ball clear or fall short of the crossbar? b.) Does the ball approach the crossbar while still rising or while falling?

    So far, I have drawn my sketch of the problem and I have chosen the x-y origin to be at the point the football is kicked, x being positive and height of crossbar (y) is positive.

    I have also drawn out a vector right angle triangle to find the trigonometric relationship between Vnaught-x, Vnaught-y, and Vnaught. From the problem, Vnaught = 20.0 and theta = 53.0 deg. I now have solved Vnaught-x to be 12.04 and Vnaught-y to be 15.97. Is Vnaught-y the max height of the ball at a distance of 12.04 meters from the origin? If so, where do I go from here?

  2. jcsd
  3. Sep 24, 2004 #2


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    Homework Helper

    You might want to calculate the time at max height, so you can tell if the ball is falling or rising when it crosses the crosshair. Also consider evaluation Y when x= 36, so you can see how high will the ball be, and if it will be higher than 3.05 m.
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