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Homework Help: Area Moment of Inerita simple rectangle composite I'm lost

  1. May 23, 2010 #1
    1. The problem statement, all variables and given/known data

    Determine the moments of the inertia of the Z-section about its centroidal x0 and y0 axes.
    I didn't draw them in, but the x0 axis is 80[mm] up from the bottom and the y0 axis is 90[mm] from the left most point. So it is in the middle of the piece.

    3. The attempt at a solution

    So I guess I'm confused as to whether or not I need to even set up this chart since its only asking for [tex]\bar{I}x[/tex] and [tex]\bar{I}y[/tex]. Its just the sum of each from the three different parts? If I do need the chart, what is dx a distance from/to? I dont think my numbers are right at all.

    I have the answers in the book.
  2. jcsd
  3. May 24, 2010 #2


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    Your values for dx an dy appear correct (d = distance from centroid of area to centroid of shape). But your chart is missing the Ix and Iy values, of the areas you designate as 1 and 3, about their individual centroids. You need the parallel axis theorem to compute the Ix and Iy of the overall shape.
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