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Length of a Pendulum

  1. Jan 29, 2012 #1
    1. The problem statement, all variables and given/known data

    A 319g ball is tied to a string. It is pulled to an angle of 7.60 degrees and released to swing as a pendulum. A student with a stopwatch finds that 14 oscillations take 13.0s.
    What is the length of the string?

    2. Relevant equations
    I have already tried using T = 2pi sqrtL/g, but that does not give me the right answer.


    3. The attempt at a solution
     
  2. jcsd
  3. Jan 29, 2012 #2

    jedishrfu

    Staff: Mentor

    Show your work so we can see what you did.
     
  4. Jan 29, 2012 #3
    13 oscillations/14 seconds = 1.07 for T, and 1/1.07 = 0.928s for f.
    Then I tried T = 2pi sqrt L/g, so 1.07 = 6.28 sqrt L/9.8m/s, then divided each side by 6.28 and got 0.170 = sqrt L/9.8, then squared each side, so 0.029 = L/9.8, then solve for L = 0.2842m, which is wrong according to MasteringPhysics.
     
  5. Jan 29, 2012 #4

    jedishrfu

    Staff: Mentor

    How far off is your answer?

    It looks okay to me. Is the g value for earth or some other planet?
     
    Last edited: Jan 29, 2012
  6. Jan 29, 2012 #5
    I figured it out...I had period and frequency backwards
     
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