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Help Deriving formula for moment of inertia lab

  1. Jul 14, 2008 #1


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    this lab is very similar to mine
    basically i can only seem to derive a portion of the formula, I=mgb/al - mb^2
    where b- radius, g-gravity, al- angular acceleration.
    I do not get the right answer:
    here is what i did do however,
    T-mg=-ma (acceleration is downwards)
    so T=(mg-ma)
    so then

    Tnet=I*al (where al is angular acceleration not acceleration)

    so then
    (b*mg-b*ma)/al = I

    as u can see this is not the correct solution..but is a start
    the solution i need to get to is
    I=mgb/al - mb^2

    can someone help me out - thanks :)
    Last edited: Jul 14, 2008
  2. jcsd
  3. Jul 14, 2008 #2


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    NEVERMIND I SOLVED IT i was on the right way i just realized that a=al*R and if i plug that in my answer is correct.
    thanks to any1 who viewed it anyways
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