Question

The theorem of perpendicular axes is not applicable for determination of moment of inertia along the diameter, for which of the following body:-

• A. sphere
• B. disc
• C. ring
• D. blade

Answer 1

The correct option is A sphere

Perpendicular axis theorem is applicable only to planar bodies. The bodies which are flat with very less thickness or negligible thickness. Hence, this theorem is not applicable in case of sphere.

According to this theorem,

The moment of inertia of a planar body about an axis perpendicular to its plane is equal to the sum of its moments of inertia about two perpendicular axes lying in the plane of the body.

$I_z=I_x+I_y$

Hence, sphere is correct answer.