What is the radius of gyration of a circular disc of radius $R$ about an axis passing through its center and perpendicular to its plane?

Three uniform similar rods of length $L$ and mass $m$ are joined to form an equilateral triangle. Find the radius of gyration about an axis passing through one corner and perpendicular to the plane of the triangle.

Two iron solid discs of negligible thickness have radii $R_1$ and $R_2$ and moments of inertia $I_1$ and $I_2$,respectively. For $R_2 = 2 R_1$,the ratio of $I_1$ and $I_2$ would be $1 / x$,where $x = $ . . . . . . .

The moment of inertia of a sphere of mass $M$ and radius $R$ is $I.$ If $M$ is kept constant and a graph is plotted between $I$ and $R,$ then its form would be:

Two discs of same mass and same thickness have densities as $17 \, g/cm^3$ and $51 \, g/cm^3$. The ratio of their moment of inertia about their central axes is .........

The ratio of the radii of gyration of a circular disc to that of a circular ring,each of same mass and radius,around their respective axes is