# Statics of Rigid Bodies.

• Jan 28th 2008, 08:42 AM
Sarah.
Statics of Rigid Bodies.
Mechanics module from Maths alevel. Three questions from the Statics of Rigid Bodies topic.

http://i18.photobucket.com/albums/b1...all/maths1.png

http://i18.photobucket.com/albums/b1...all/maths2.png

http://i18.photobucket.com/albums/b1...all/maths3.png

Any help would be appreciated. I've gathered that you have to use those horrible integral formulars and rho. xx
• Jan 28th 2008, 09:35 AM
TKHunny
I suggest that you have gathered correctly. Feel free to demonstrate it. Well, you have one thing not quite right. The formulas aren't that bad. Just do it.

Let's see what you get.
• Jan 28th 2008, 10:44 AM
Sarah.
If you want to see some horrible maths...

7.

Mx = Intergal between r and 0 of x root(r^2 -x^2) dx

= -2/6 (r^2 - x^2)^3/2 = -2/6
-
=(r^2)^3/2 = -2/6 r^4/3

/ 1/4 pi r^2

Am I on the right lines?
• Jan 28th 2008, 12:13 PM
TrevorP
I did 11 actually for my last math homework. Here are the basic integrals:

$Centroid: (\overline{x}, \overline{y})$

$\overline{x} = \frac{\int_0^1 x(x - x^2)dx}{\int_0^1 (x-x^2)dx}$

$\overline{y} = \frac{\int_0^1 y(\sqrt{y} - y)dy}{\int_0^1 (x-x^2)dx}$

I'm not going to tell you the answer though. But they should be clean decimals.
• Jan 28th 2008, 12:57 PM
Sarah.
Quote:

Originally Posted by TKHunny
I suggest that you have gathered correctly. Feel free to demonstrate it. Well, you have one thing not quite right. The formulas aren't that bad. Just do it.

Let's see what you get.

I suppose this was more like moral support than anything but thanks all the same. I managed to solve them. x
• Jan 28th 2008, 01:47 PM
TKHunny
You didn't do ALL the integrals for the middle one, did you? I hope you exploited the symmetry in the horizontal direction.