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Homework Help: Projectile motion in serious need of help

  1. Sep 12, 2011 #1
    I need loads of help, i have a physics test on friday and have been studying vigorously; i havent been lazy and have been working fopr 8 weeks, i tried to do this question and i have no clue HELP ME PLEASE!!!

    1. The problem statement, all variables and given/known data

    A place-kicker must kick a football from a point
    36.0 m (about 40 yards) from the goal, and half the crowd
    hopes the ball will clear the crossbar, which is 3.05 m high.
    When kicked, the ball leaves the ground with a speed of
    20.0 m/s at an angle of 53.0° to the horizontal. (a) By how
    much does the ball clear or fall short of clearing the crossbar?
    (b) Does the ball approach the crossbar while still rising
    or while falling?

    3. The attempt at a solution
    Ok so i found the velocity of the x component using simple trig but then im in trouble with the next step. i have absolutely no clue at all i tried to find the time it takes to cover the x displacemetn at the x velocity then used that time to find the overall displacement.
  2. jcsd
  3. Sep 12, 2011 #2
    Solve the y displacement instead using the time you got. The time you got is the time at which the ball is at x = 36.0 m, so the next step would be to calculate the height of the ball at that time. Then compare that height to the height of the crossbar and answer question a.
  4. Sep 12, 2011 #3
    thank you sooo much You honestly dont know how much that means i was stressing out big time because the test is thursday and im fixing up my weaker points...

    I did what you said and the answer is correct

    Once again thanks so much
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