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Homework Help: What is the tension in the string at the bottom of the swing?

  1. Feb 14, 2008 #1
    A pendulum is 0.6 m long and the bob has a mass of 1.0 kg. At the bottom of its swing, the bob's speed is 1.9 m/s. What is the tension in the string at the bottom of the swing?

    The attempt at a solution
    I did Newtons second law F=ma. So I tried:

    The sum of all forces=ma

    I figured the acceleration would be zero when it is at the bottom of the swing. I have tried many different answers and can't seem to come up with the right one. Please help!
  2. jcsd
  3. Feb 14, 2008 #2

    Doc Al

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    Staff: Mentor

    The acceleration is not zero at the bottom of the swing. Hint: What kind of motion does the bob undergo?
  4. Feb 14, 2008 #3
    I am not exactly sure, but you might be able to use the equation v = sqrt(Forcetension/(m/L)).

    I dont know how you derive this formula, but this is one of the formulas they give in my physics book (im actually doing the same thing right now in my class), so this should be what your looking for.

    The acceleration would be zero only when the velocity is at it's max (I think).

    Hope that helps.
  5. Feb 14, 2008 #4
    I know it is nonuniform circular motion. But I still don't get it.
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