The moment of inertia of a uniform circular disc about its diameter is $I$. What is its moment of inertia about an axis perpendicular to its plane and passing through a point on its rim (in $, I$)?

$A$ system of five solid spheres, each of mass $m$ and radius $r$, is rotating about an axis $AA'$. The moment of inertia of the system about the axis of rotation $AA'$ is: (in $mr^2$)

$A$ square lamina of side $b$ has the same mass as a disc of radius $R$. The moment of inertia of the two objects about an axis perpendicular to the plane and passing through the centre is equal. The ratio $\frac{b}{R}$ is

Three spheres,each of mass $m$ and radius $r$,are placed as shown in the figure. Consider an axis $YY^1$,which is tangent to two spheres (labeled $2$ and $3$) and passes through the diameter of the third sphere (labeled $1$). The moment of inertia of the system consisting of these three spheres about the $YY^1$ axis is:

$A$ uniform circular disc of radius $R$ and mass $M$ is rotating about an axis perpendicular to its plane and passing through its centre. $A$ small circular part of radius $R/2$ is removed from the original disc as shown in the figure. Find the moment of inertia of the remaining part of the original disc about the axis as given above.

$(a)$ Prove the theorem of perpendicular axes. (Hint: Square of the distance of a point $(x, y)$ in the $x-y$ plane from an axis through the origin and perpendicular to the plane is $x^{2}+y^{2}$)
$(b)$ Prove the theorem of parallel axes. (Hint: If the centre of mass of a system of $n$ particles is chosen to be the origin,$\sum m_{i} r_{i}=0$)