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Homework Help: Problem with tether balls - How high should I release the ball

  1. Apr 28, 2004 #1
    hi, im a grade 12 student and am stuck on this question. could somebody help me solve it or solve it for me.
    the question is:
    A 1 kg tether ball is suspended by a string .8 m long from a nail a point X, .5 m vertically above a horizontal rob at Y. when the ball is released from Z, it swings down and the string catches on Y. how high above Y must the tether ball be released so that it will swing completely around a circle of a radius .3 m about point Y.
  2. jcsd
  3. Apr 29, 2004 #2


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    Science Advisor

    At its lowest point, .8 m below X, the ball must have enough kinetic energy that, after it has "caught" on y and swings to its highest point .3m above y (and so .6 m above its lowest point- .2 m below X, it still has some kinetic energy left to "get over the top".
  4. May 1, 2004 #3

    Doc Al

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    Staff: Mentor

    Careful... the amount of KE that must be left at the top is non-zero: there is a mimimum amount needed to keep the string taut. (Hint: releasing the ball 0.3m above Y will not give it enough speed.)
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