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Homework Help: MI of rectangular and triangular lamina

  1. Feb 21, 2009 #1
    1. The problem statement, all variables and given/known data

    can anyone please send me the link to calculate the moment of inertia of cuboid,rectangular and triangular lamina ??(along with figure)
    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 21, 2009 #2


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    Homework Helper

    Welcome to PF.

    Just use the formula:

    I = ∫ r2 dm

    Taken over all the mass elements.

    Since you are interested in lamina then you're only interested in two dimensional area density.
  4. Feb 22, 2009 #3
    thank you so much for your help..
    while deriving the formula for rectangular lamina,of sides 2a and 2b(i.e.,length 2a and breadth 2b),when i consider a thin horizontal strip parallel to x-axis at distance y from x-axis and infinitesimally small thickness dy,
    after using the formula you have given..what limits of the integral should i take??please help..
    one last thing i need to know is that in the link which you have sent,under extended explanation someone's written
    WARNING: there is no such thing as moment of inertia about a point
    and then the definition of moment of inertia about a point is mentioned...if there's no such thing as moment of inertia about a point then how do we define MI in 1 dimension??
    like MI in 2-d is about a line and MI in 3-d is about coordinate axis..then in 1-d is it not supposed to be about a point??
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