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Angle theta baseball problem

  1. Jan 17, 2010 #1
    1. The problem statement, all variables and given/known data
    A boy throws a ball upward with a speed of vo= 12m/s. The wind imparts a horizontal acceleration of 0.4m/s^2 to the left. At what angle theta must the ball be thrown so that it returns to the point of release. (assuming wind does not affect vertical motion.

    2. Relevant equations
    All physics equation

    3. The attempt at a solution
    I have written down all the formulas in the x and y directions, but it doesnt work out. I have also tried to look for what distance Vy=0 but i still end up having 2 unknowns.
  2. jcsd
  3. Jan 17, 2010 #2


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    Hi Larrytsai! :smile:

    (have a theta: θ and try using the X2 tag just above the Reply box :wink:)

    You should have only two unknowns, θ and t, so two equations should be enough.

    Show us your full calculations, and then we can see what went wrong, and we'll know how to help! :smile:
  4. Jan 17, 2010 #3
    Re: Physics

    ok so what i have so far is,
    for y:
    y= (1/2 a t^2) + (Vo cosθ t)
    (Vcosθ)^2 = (Vocosθ)^2 + 2ay

    for x:
    x= (1/2 a t^2) + (Vo sinθ t)
    (Vsinθ)^2 = (Vosinθ)^2 + 2ax

    so far how i see it is im going to substitute my 2 x equations and my 2 y equations, then ill have 2 equations left to subtitute which are θ and time.
  5. Jan 17, 2010 #4


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    (hmm … the second and fourth equations are just V = V0 … that doesn't help much)

    What's the difficulty?

    Put all the numbers in, including x = y = 0, and what do you get? :smile:
  6. Jan 17, 2010 #5
    Re: Physics

    ohh ok, i got the answer, thnx so much, but im a little confused as to why x is 0, im thinking that when the height and horizontal distance is 0 , the ball has landed back in the boys hand, therefore the time elapsed is the same so we can subsitute for time?

    btw thanx alot
  7. Jan 17, 2010 #6


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    Hi Larrytsai! :smile:

    Yes, you're getting confused.

    When the ball returns to the hand, both x and y are 0, and the time elapsed is t (say).

    So the same t appears in both the equation for x and the equation for y.
  8. Feb 12, 2010 #7
    Re: Physics

    What substitutions were made?
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