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Moment of inertia of a "thick" sphere Find the moment of inertia of a solid of constant density $$\delta$$ bounded by two concentric spheres of radii $$a$$ and $$b ( a < b )$$ about a diameter.
$$I _ { z } = \frac { 8 \pi \delta ( b ^ { 5 } - a ^ { 5 } ) } { 15 }$$