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Homework Help: Find tension of string in a pendulum

  1. Oct 17, 2007 #1
    1. The problem statement, all variables and given/known data

    A pendulum is 0.615 m long and the bob has a mass of 1.37 kg. When the string makes an angle of =14.1° with the vertical, the bob is moving at 1.40 m/s. Find the tangential and radial acceleration components and the tension in the string. [Hint: Draw an FBD for the bob. Choose the x-axis to be tangential to the motion of the bob and the y-axis to be radial. Apply Newton's second law.]
    at = _____m/s2
    ar = _____ m/s2
    T = _______ N

    2. Relevant equations


    3. The attempt at a solution

    I have tried breaking up the forced using the FBD but I cannot get the right answer for any of them. I have no idea what I am doing wrong. For the tangential acceleration i got: 6.54 and 6.74 doing it two different ways. For tension I got 13.02 N and those are still not correct...
  2. jcsd
  3. Oct 18, 2007 #2
    In the y (radial) direction there is T and a component of gravity.
    In the x (tangential) direction, there is only the other component of gravity.

    So figure out Fnet in the tangential direction then Fnet in the radial direction.
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