Question

Seven identical circular planar disks, each of mass $M$ and radius $R$ are welded symmetrically as shown. The moment of inertia of the arrangement about the axis normal to the plane and passing through the point $P$ is?

Answer 1

$I_o=I_{cm}+m{d}^2$

$=\frac{7M{R}^2}{2}+6(M\times (2R{)}^2)$

$=\frac{55M{R}^2}{2}$

$I_p=I_o+m{d}^2$

$=\frac{55M{R}^2}{2}+7M(3R{)}^2$

$=\frac{181}{2}M{R}^2$