Finding Centroid and Second Moment of Area for Complex Sections

[Chantry09]

Im having a hard time getting my head around this, any help would be much appreciated.

Homework Statement

Determine the position of the centroid and calculate the second moment of area about a horizontal axis passing through the centroid for the following sections shown. Attached is the image of the shape, including dimensions.

Homework Equations

A x Y(bar) = (A1 x Y1) + (A2 x Y2)
IX = Ix + Ah(squared) [Not sure if this equation is correct]

The Attempt at a Solution

I know Y(bar) to equal 40mm for the attached shape. However i don't know how to get from the y(bar) to the position of the centriod. The answer should be 862000.0mm, i just don't know how to get there, everything i try comes up with a different result.

 

[HallsofIvy]

Well, you have me confused! (Not all that difficult.) In most textbooks, "Y(bar)" (\overline{Y}[/tex]) <b>means</b> the y-component of centroid. I, frankly, don&#039;t see how you could have gotten 40 mm. That&#039;s only a little bit above the bottom line. You do understand, don&#039;t you, that the &quot;centroid&quot; of a figure is the geometric center? If this, very symmetric, figure goes from 20 mm at the bottom to 120 mm at the top, 10mm on the left to 80 on the right, where do you think center is?

 

[Chantry09]

Yeah [PLAIN]https://www.physicsforums.com/latex_images/16/1615993-0.png is what i meant, i couldn't find the symbol. My diagram might not be clear, but the height is 80mm and considering its symetric in the x and y direction i thought [PLAIN]https://www.physicsforums.com/latex_images/16/1615993-0.png = 1/2 total height?

Is that not right?

 

[Chantry09]

Bump. On my hands and knees here guys :S