Question

On Pset 7, section 3:C, on problem #3, why do the solutions integrate JUST "rcos(theta)" and "Y," when moment of inertia = (integral of) [r^2 dm] ??

I know from physics that I=(integral of)r^2dm, and calculating it with single integrals is fairly straightforward. So what's going on here??

What I mean is, in both parts, the arm from the point of rotation to the farthest point on the section of the circle is Y or rcos(theta). So why are they not using Y^2 and (rcos(theta))^2 ???

Answer 1

I think they made a mistake.

Answer 2

HA!! "Ladies and gentlemen.. we got 'em!"

Good.. I was going crazy trying to figure out why they weren't using the square of the lever arm.

Answer 3

THANKS!