# Moment of inertia of a sphere (Is this right?)

1. Nov 8, 2009

### een

1. The problem statement, all variables and given/known data
A homogenous punctured sphere with inner radius a and outer radius b rotates around an axis that touches its outer surface. Determine the moment of inertia. [hint: use the parallel axis theorem]

2. Relevant equations

3. The attempt at a solution
basically i used... {($$\rho$$,$$\theta$$), a<$$\rho$$<b, 0<$$\theta$$<2pi), d(p,c) =$$\rho$$cos$$\theta$$

I = $$\int$$0-2pi$$\int$$a-b (M/(pi(b^2-a^2)))$$\rho$$^2*cos^2$$\theta$$*$$\rho$$*d$$\rho$$d$$\theta$$

I simplified and got I = M(5b^2+a^2)/4...IS THIS RIGHT???