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Second moment of area

  1. Mar 12, 2013 #1
    Find the second moment of area about the vertical axis for the cross-section of the follwing shape.

    i cant get the pic to paste so will describe it:

    it is a rectangle of horizontal length 8 and vertical height 6.

    if we let (0,0) be at the lhs bottom corner, then a circle has been cut out with
    centre at (5,3)

    i have no idea how to go about this. one web page says i need integral y^2dxdy another just used the c of mass of one shape and the other shape (was L shape). (so here i would need com of rectangle- com circle)

    any help would be much appreciated.
  2. jcsd
  3. Mar 12, 2013 #2
    Hello, does the photo look like the one I attached?

    Attached Files:

    • Pic.jpg
      File size:
      10.3 KB
  4. Mar 13, 2013 #3
    almost, the picture i have has the circle more towards the rhs of the rectangle.
  5. Mar 13, 2013 #4


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    So, what is the question? What are you trying to find, the center of mass of the object?
  6. Mar 13, 2013 #5


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    You don't give the radius for the circle.
    For the second moment about a vertical axis, don't you need to integrate x2dydx? And you might want that taken about the x coordinate of the mass centre.
  7. Mar 14, 2013 #6
    as in my first post, i am trying to find the second moment of area about the vertical axis
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