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Homework Help: Rotation at an angle - Tether ball (Finding length)

  1. Feb 27, 2012 #1
    1. The problem statement, all variables and given/known data
    A tether ball is a ball at the end of a rope tied to a pole 3m tall. A player whips the ball around with a speed of 9.5 m/s and the string rises to an angle of 32°. Find the length of the string.

    length of pole = 3m
    v = 9.5
    angle θ = 32°

    2. Relevant equations
    Fnet = ma

    3. The attempt at a solution
    I drew the FBD on the diagram itself

    http://sadpanda.us/images/857602-GFGQJ1G.jpg [Broken]

    I know I did something wrong because the radius I got is way too big.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Feb 27, 2012 #2


    User Avatar

    Staff: Mentor

    Actually, your value matches the given information of angle and velocity. It doesn't accord very well with the supposed 3m height of the pole though! And it gets worse when you consider that 14.7m is just the radius of rotation; the string length h will be about twice that!

    Looks like a problem with the problem itself, not your work :smile:
    Last edited by a moderator: May 5, 2017
  4. Feb 27, 2012 #3
    Oh, damn.. I left the next question cause it was the same idea.

    So to calculate h ot wpi;d ne

    Fx = 14. 7m

    14.7 h
    ----- = ----
    sin32 sin 90

    h = 27.7 m?
  5. Feb 27, 2012 #4


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    Staff: Mentor

    That looks about right :wink:
  6. Feb 27, 2012 #5
    Thanks a lot, that damn question threw me off.

    Anyways, I'm off to bed. G'night everyone who reads this :)
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