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Homework Help: Rotational inertia again!

  1. Nov 3, 2005 #1
    Please take a look at this:

    Calculate the rotational inertia of a section of a right circular cylinder of radius R that subtends an angle of 'theta knot' at the origin when the reference axis is at the origin and perpendicular to the section.

    I tried to draw the picture in the attachment.
    I tried to use the formula I=Integral(R2*dm), with dm =density*dV
    where V is the volume. I would like to know if I am in the good direction

    Thank you for your help


    Attached Files:

  2. jcsd
  3. Nov 3, 2005 #2


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    Science Advisor
    Homework Helper

    Lol, isn't it 'theta naught'? As in [itex]\theta_0[/itex]?

    [tex]I=\int_V R^2\rho dV[/tex]
    is always correct. You should go to cilindrical coordinates for this problem.
  4. Nov 9, 2005 #3

    Hi I am still stuck with with problem of inertia . please can someone help me.
    Can you give me more suggestions
  5. Nov 9, 2005 #4
    If I understand the question correctly, maybe this will help
    [tex]\int_V R^2\rho dV =\rho \int_V r^2 r dr d\phi dz[/tex]
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