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Homework Help: Kinematics Plz help

  1. Oct 9, 2007 #1
    kinematics urgent Plz help

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

    A quarterback claims that he can throw the football a horizontal distance of 183 m (200 yd). Furthermore, he claims that he can do this by launching the ball at the relatively low angle of 30.0° above the horizontal. To evaluate this claim, determine the speed with which this quarterback must throw the ball. Assume that the ball is launched and caught at the same vertical level and that air resistance can be ignored. For comparison, a baseball pitcher who can accurately throw a fastball at 45 m/s (100 mph) would be considered exceptional.

    2. Relevant equations

    183 = UxT
    Ucos30T=183 (1)

    Uy = Usin30
    AT + V = Uy
    0=Uy-9.8T Uy-0 = 9.8T
    Uy-9.8T=0 Uy - 9.8T = 0
    Usin30-9.8T=0 Usin30 - 9.8T = 0
    T=Usin30/9.8 (2) T = Usin30/9.8 (2)

    (2) into (1):
    Ucos30*Usin30/9.8=183 * = 183 Ucos30 Usin30/9.8
    U^2 cos30sin30=1793.4 U ^ 2 = 1793.4 cos30sin30
    U^2=4141.7 U ^ 2 = 4141.7
    U=64m/s U = 64 m / s

    3. The attempt at a solution

    Is this right plz help...and U = V

    plzzzzzzzzzzzzzzzzz help
  2. jcsd
  3. Oct 9, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    T=Usin30/9.8 is the time to get to the peak of the trajectory. It must take the same time to get down to the same initial elevation, neglecting air resistance.
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