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## Homework Statement

A hollow sphere has a mass of 15 kg, an inner radius of 12 cm and an outer radius of 18 cm. What is the rotational inertia (moment of inertia) of the sphere about an axis passing through its center?

## Homework Equations

## The Attempt at a Solution

I = 2/3 MR^2 for a hollow sphere so i did this:

2/3 (15) (.18^2) = .32 kg m^2

But this is wrong the answer is .24 kg m^2.

Any thoughts?