1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    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


    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook