Statics, moment of inertia simple square-shape (no calculus)

[Femme_physics]

Statics, moment of inertia simple square-shape...need help (no calculus)

Homework Statement

Calculate the moment of inertia to the central axes Xc and Yc for the sketched cross-section.

Xc = 33.9 mm
Yc = 150 mm


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Homework Equations

Moment of inertia geometrical shapes. No calculus.

Answers are

Ix = 1.008 x 10^8 mm^4
Iy = 1.085 x 10^7 mm4

The Attempt at a Solution

attached. I accidentally wrote Yc in the last equation instead of Iy...

 

[I like Serena]

Your horizontal distance of the smaller rectangle has been taken as if it was horizontally centered, but it's not...

 

[Femme_physics]

I've been trying to think what you mean but I'm not sure. Are my distances incorrect?

 

[I like Serena]

I've been trying to think what you mean but I'm not sure. Are my distances incorrect?

You have your distances as:
(125/2-33.9) for the larger rectangle, but (110/2-33.9) for the smaller rectangle.
The latter is incorrect.

Perhaps if you draw it on paper (accurately enough), you can measure the distances and you'll see what I mean.
Note that it's always useful to make drawings like that if only to verify no mistakes were made.

 

[Femme_physics]

Got it! So the distance should be 125-110/2-33.9 = 36.1.

Yep, right answer now :D Merci me amora!