Weird question, with strength of materials (probably)

[berdan]

Hi,
So,I'm helping a guy with his mechanical engineering homework.
The problem is that the guy is so off, he doesn't even know the name of the subject.
And honestly, I having a hard question finding out what this question is about.
I need to proove the Zb=h^2/3 thingy. I have no idea what this is about.

Can someone point me to the subject?

 

[robax25]

it is just a rectangle.

 

[PhanthomJay]

Sort of a funky sketch, but I would say what you have here is 2 vertical parallel lines (bars) of unit width and height h, separated by a distance b, and you are looking for the Section Modulus of those parallel bars about the x-axis passing through its center of gravity. Section Modulus is commonly denoted as S (or sometimes Z) where S is equal to the moment of inertia of the bars about the cg and x-axis divided by the vertical distance from the cg to the top of the bars. In which case from tables I is h^3/12 for each bar, twice that for 2 bars, h^3/6. Thus S is h^3/6 divided by h/2, or h^2/3. I’m just guessing though, and in any case it won’t be of much help to him if the whole course is way beyond him, and he should probably choose another career perhaps or get his act in gear.

 

[berdan]

Sort of a funky sketch, but I would say what you have here is 2 vertical parallel lines (bars) of unit width and height h, separated by a distance b, and you are looking for the Section Modulus of those parallel bars about the x-axis passing through its center of gravity. Section Modulus is commonly denoted as S (or sometimes Z) where S is equal to the moment of inertia of the bars about the cg and x-axis divided by the vertical distance from the cg to the top of the bars. In which case from tables I is h^3/12 for each bar, twice that for 2 bars, h^3/6. Thus S is h^3/6 divided by h/2, or h^2/3. I’m just guessing though, and in any case it won’t be of much help to him if the whole course is way beyond him, and he should probably choose another career perhaps or get his act in gear.

You are absolutely right in all accounts. Funny thing is that I wasn't aware of this as well, being a Mechanical Engineer with a diploma hah.
Thanks a lot!