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Homework Help: 2 dimension kinematics Cutnell Chapter 3 Prob 26

  1. Sep 27, 2007 #1
    1. The problem statement, all variables and given/known data

    A quarterback claims that he can throw the football a horizontal distance of 184 m. Furthermore, he claims that he can do this by launching the ball at the relatively low angle of 29.7 ° 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
    .5*184m=92m -adjacent side
    90-29.7(theta)=60.3 other angle
    Hyp=x/cos theta or 91.42=92/.8686
    Opposite ; tan theta=X/92(adjacent side)=54.27 is (.5704*92)

    need time so d=(.5)at^2
    184=(.5)(-9.80)(t)^2 =-6.13seconds

    3. The attempt at a solution

    see above - I'm not sure I have the time set up properly. I need a hint as to how to get
    started with determining the velocity - just a hint!!
  2. jcsd
  3. Sep 27, 2007 #2


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    Science Advisor

    Use an equation for Projectile Motion instead.
  4. Sep 27, 2007 #3
    Split the velocity vector on x and y component. Then it's easy to calculate the time of flight since x speed is constant. Once you have time, you have tu calculate what initial y speed should be that the vertical throw with that speed would be that long.
  5. Sep 27, 2007 #4


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    Science Advisor

    Since the problem is stated this way, the horizontal displacement is the range. Thus, use a projectile motion equation for the range.

    It will then be a very simple problem of substituting in the given values!
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