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Homework Help: SHM of a pendulum

  1. May 1, 2014 #1
    1. The problem statement, all variables and given/known data
    A uniform steel bar swings from a pivot at one end with a period of 1.2 seconds. How long is the bar?


    2. Relevant equations
    T=2[itex]\pi[/itex][itex]\sqrt{L/g}[/itex]


    3. The attempt at a solution
    I manipulated this equation to solve for L, giving me L=[itex]T^{2}g/4\pi^{2}[/itex]
    Plugged in T=1.2 seconds and g=9.8. Answer I got was (to two significant figures) 0.36 m. But apparently that answer is wrong so I don't know what I am missing or if I am using the wrong equation.
     
  2. jcsd
  3. May 1, 2014 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The equation you are using is for a simple pendulum, where all the mass is concentrated at the end. When the mass is spread out, as in your problem, you have what is called a physical pendulum, so you'll need to modify that formula a bit. Read this: Physical Pendulum
     
  4. May 1, 2014 #3
    That clears things up a bit. I got the answer now. Thanks.
     
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