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Finding frequency if you know mass and length of rope.

  1. Nov 7, 2013 #1
    1. The problem statement, all variables and given/known data

    A girl with a mass of 40 kg is swinging from a rope with a length of 2.8 m. What is the frequency of her swinging?

    2. Relevant equations

    I could find the period of the situation and then from there could calculate the frequency. For the period I'm not sure what equation I should use. I tried using the equation T=2∏ (√I / mgh ). This did not work for me though. Any help would be nice!

    3. The attempt at a solution
    Attempt shown above.
  2. jcsd
  3. Nov 7, 2013 #2

    Doc Al

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    Staff: Mentor

    That's the formula for a physical pendulum, which should work just fine. Show what you did.

    Of course, since you are ignoring the mass of the rope (I presume), you can also treat this as a simple pendulum.
  4. Nov 7, 2013 #3
    Okay I used the equation for a simple pendulum: T= 2 x pie x square root of L / g. Square root of 2.8 / 9.8 x 2pie gave me 3.35 for a period. Then I plugged in 1/3.35 for the frequency and came up with the right answer. Thanks so much!
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