# Second moment of area

1. Mar 12, 2013

### jiboom

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. Mar 12, 2013

### mishek

Hello, does the photo look like the one I attached?

#### Attached Files:

• ###### Pic.jpg
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3. Mar 13, 2013

### jiboom

almost, the picture i have has the circle more towards the rhs of the rectangle.

4. Mar 13, 2013

### HallsofIvy

So, what is the question? What are you trying to find, the center of mass of the object?

5. Mar 13, 2013

### haruspex

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.

6. Mar 14, 2013

### jiboom

as in my first post, i am trying to find the second moment of area about the vertical axis