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Do I use a system of equations for this projectile motion?

  1. Dec 18, 2006 #1
    1. Chuck Norris kicks a basketball from the ground into a basketball hoop, it makes it in perfectly. THe hoop is 150m away, and 6m above the ground. He kicks the ball at a 39 degree angle. How long does it take for the ball to reach the net? What was the initial velocity?

    2. X1=X0+v0t+1/2at^2

    3. So breaking it down, I know that Vox = v0cos(39)
    And that voy= v0Sin(39

    Doesn't that mean I use the tangent function? Can somebody jumpstart my memory? :frown:
  2. jcsd
  3. Dec 18, 2006 #2
    A little background:
    As a homework assignment, we were told to make up a moderate problem and share with the class as a review for upcoming midterms. I solved one of these a few months ago and cannot remember at all how.
  4. Dec 18, 2006 #3


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    Staff Emeritus
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    Your components of velocity are correct. Try writing your equation out twice; once for vertical and once for horizontal motion.
  5. Dec 18, 2006 #4

    Doc Al

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    Staff: Mentor

    That's a good generic equation. Hint: Write separate equations for the horizontal and vertical motions. (How do they differ?)

    This is good. Combine this with the above equations and you'll be able to solve for V0.
  6. Dec 18, 2006 #5
    Once you write the equation for the horizontal motion, try to solve it to get [itex]v_0t[/itex] and substitute it in the equation for verticle motion. This will give you time! Try it!
  7. Dec 18, 2006 #6
    150=0+v0Sin(39) + 1/2*0*t^2
    6=0+v0Cos(39) + 1/2*-9.81t^2

    From here, doesn't tangent end up replacing Sin and Cosine though?
  8. Dec 18, 2006 #7

    Doc Al

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    Staff: Mentor

    You've mixed up your sines and cosines.

    No. You know the sine and cosine, so they are just numbers. Combine the two equations and solve for v0.
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