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## Homework Statement

Find the moment of inertia of a torus if mass is m and density [itex]\rho[/itex] is constant.

The cross-sectional radius is 'a' and the radius is R.

## Homework Equations

[tex]I= \int r^2 dm[/tex]

## The Attempt at a Solution

Well I looked up the answer to be

[tex]I_z= m(R^2 + \frac{3}{4}a^2)[/tex]

But I am not sure how to start. Can someone just point me in the right direction?