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Homework Help: Circular motion!

  1. Feb 20, 2008 #1
    ***circular motion!***

    1. The problem statement, all variables and given/known data
    A 3.60 kg object is attached to a vertical rod by two strings as in Figure P6.11. The object rotates in a horizontal circle at constant speed 7.20 m/s.

    (a) Find the tension in the upper string.

    (b) Find the tension in the lower string.

    2. Relevant equations


    3. The attempt at a solution

    I tried to solve for r and i got 1.32 but when i plugged it into the equation for tension it said it was wrong. i tried to solve for theta and got 41.3 in order to plug into the equation and it was wrong as well. what am i doing wrong??
  2. jcsd
  3. Feb 20, 2008 #2


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    Homework Helper

    I think you are forgetting there are two strings. You can't use your equation and do each string separately. You need two different tension forces in your equations. Draw a free body diagram of the ball and sum up the forces in each direction like you would do for any other force problem.
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