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Homework Help: Time for a ball on string to travel around a pole.

  1. Oct 17, 2012 #1


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

    A tetherball with a string length of 1.5m is hit in such a way that it completes a circle around the pole with the string at 30 degrees from the pole. Assuming it doesn’t lose a significant length during the trip around the pole and hence takes a perfectly circular orbit, what is the time period for a circuit around the pole for the ball? (Remember the acceleration caused by the string has to have a y component such that it completely counteracts the gravity).

    2. Relevant equations

    c=2pir //for the circumferences of the sircle it travels.
    xsinθ // distance from the pole to the ball, x direction only
    ycosθ // distance from the ball to the top of the pole, y direction only

    3. The attempt at a solution

    I really only got what I have listed above.
    x=0.75m , y≈1.299m , c≈4.7124m
    I assume I'd need to figure out the force of the hit to keep it that far out from the pole, then calculate time from that, but I'm drawing a blank right now.
  2. jcsd
  3. Oct 17, 2012 #2

    Doc Al

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    Staff: Mentor

    Apply Newton's 2nd law. What forces act on the ball? What do you know about acceleration and circular motion?
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