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Homework Help: Circular Motion

  1. Jan 20, 2015 #1
    1. The problem statement, all variables and given/known data
    A .8 kg lead ball is whirled on the end of a string 5 meters long. When the ball passes through point A at the top of the path, the tension in the string is 4.96 N.
    What is the speed of the bob at point A?
    *NOTE - POINT A is at the top of the circle...

    2. Relevant equations

    3. The attempt at a solution
    v = √(F*r)/m

    V = √(4.96*5)/.8
    V = 5.57 m/s

    DOESN'T WORK...!
  2. jcsd
  3. Jan 20, 2015 #2


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    Homework Helper

    At the top of the circle, what are the forces acting and in what directions do they act (up or down) ?

    The resultant of these forces is equal to the centripetal force mv2/r
  4. Jan 20, 2015 #3
    Umm force of weight and that's all... and it acts down.
    But what does that do?
  5. Jan 21, 2015 #4
    Not just weight. Another force acts on it too. You've mentioned it in the problem itself.
  6. Jan 21, 2015 #5
    Have you drawn a free body diagram showing the forces acting on the ball, or do you feel you have advanced beyond the point where you need to use free body diagrams?
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