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Homework Help: Moment of intertia of wheel

  1. Sep 6, 2011 #1
    1. The problem statement, all variables and given/known data


    i've attched a picture of the wheel, which need to calculate moment of intertia with respect to 8 rods.

    i've tried to use stiener rule but it's not getting the answer,

    moment of wheel is (m1*r^2)/2
    moment of rod is (m2*r^2/3)

    i use the rule i total = icm + mr^2

    so it's 8*( (m1*r^2)/2 + (m2*r^2)/3 )

    what am i missing?



    2. Relevant equations

    m1 = mass of wheel
    m2 = mass of rod
    r = length of rod

    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Sep 6, 2011 #2

    Doc Al

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    Staff: Mentor

    Revisit this formula.

    There are 8 spokes but only 1 wheel.
     
  4. Sep 6, 2011 #3
    that's right, 8 * 3(m2*r^2), i refer the moment of wheel is (m1*r^2)/2 and sum them,

    but the correct answer is (3m2/8 + m1) * r^2
     
  5. Sep 6, 2011 #4

    Doc Al

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    Staff: Mentor

    (1) Your formula for the moment of inertia of the wheel portion is incorrect.
    (2) In your final result in post #1 you multiplied all terms by 8, thus counting the wheel 8 times.

    Double check that answer; looks like a typo.
     
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