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Bottom of a pendulum, what is tension

  1. Sep 24, 2006 #1
    A pendulum is 0.7 m long and the bob has a mass of 1.0 kg. At the bottom of its swing, the bob's speed is 1.6 m/s. What is the tension in the string at the bottom of the swing?

    I know that I can use centripetal force, which can be calculated from v -

    ma(c) = (mv^2)/r

    I get 3.6571 N as my answer, why is this wrong? thanks
  2. jcsd
  3. Sep 24, 2006 #2


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    The tension equals T = mv^2/r + mg.
  4. Sep 24, 2006 #3
    T= 1(1.6^2)/.7 + 1(9.81) = 13.47 N

    This is still incorrect... any other clues? thanks
  5. Sep 24, 2006 #4
    what makes you think it's incorrect? ... cause it is correct.

    at the bottom of the swing, Fnet = T - mg

    mv^2/r = T - mg

    T = mv^2/r + mg
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