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Homework Help: Tension in a string simple pendulum

  1. Jun 8, 2012 #1
    1. The problem statement, all variables and given/known data

    Hi Guys
    I obtained a slighty different answer. Can anyone kindly verify where I am going wrong? The question is stated thus:
    A simple pendulum is of length 0.5m and the bob has mass 0.25kg. Find the greatest value for the tension in the string when the pendulum is set in oscillation by drawing the bob to one side through an angle of 5 degrees and releasing from rest. Explain where in the cycle the tension is greatest.

    Te relationship for centripetal force involved is
    T-mg = mv^2/r
    Resolving the tension in the string into its components,
    Tcos theta = mg
    Tsin theta =mv^2/r
    Dividing the above, we obtain
    tan theta =v^2/gr
    So, v^2 = gr tan theta
    I substituted this value and other values for mass and g. I obtained 2.7N as my final answer. But it appears to be 2.5N. Any clarification will be appreciated. Thanks.
    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 8, 2012 #2
    When you say Tsin theta =mv^2/r, do you mean to imply that the horizontal component of tension is the centripital force?
  4. Jun 10, 2012 #3
    Yes. That is my assumption. I have a feeling it may not be valid. Is tension equal to the weight at the point of rest?
  5. Jun 10, 2012 #4
    Your are calculating the tension T at its highest position.
    Maximum tension is at its lowest position.
    At this position, the PE at the top is converted to maximum kinetic energy.
    Find this velocity from conservation of energy.
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