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Homework Help: Moment of inertia of a sphere (Is this right?)

  1. Nov 8, 2009 #1


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    1. The problem statement, all variables and given/known data
    A homogenous punctured sphere with inner radius a and outer radius b rotates around an axis that touches its outer surface. Determine the moment of inertia. [hint: use the parallel axis theorem]

    2. Relevant equations

    3. The attempt at a solution
    basically i used... {([tex]\rho[/tex],[tex]\theta[/tex]), a<[tex]\rho[/tex]<b, 0<[tex]\theta[/tex]<2pi), d(p,c) =[tex]\rho[/tex]cos[tex]\theta[/tex]

    I = [tex]\int[/tex]0-2pi[tex]\int[/tex]a-b (M/(pi(b^2-a^2)))[tex]\rho[/tex]^2*cos^2[tex]\theta[/tex]*[tex]\rho[/tex]*d[tex]\rho[/tex]d[tex]\theta[/tex]

    I simplified and got I = M(5b^2+a^2)/4...IS THIS RIGHT???
  2. jcsd
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