Question

A planar body is lying in the xz plane. What is the relation between its moment of inertia along the x, y & z axes?

(a) Iz = Ix + Iy

(b) Ix = Ix + Iz

(c) Iy = Ix + Iz

(d) Iz = Ix = Iy, because body is planar

The question was posed to me in an online quiz.

I'm obligated to ask this question of Theorems of Perpendicular and Parallel Axes topic in section System of Particles and Rotational Motion of Physics – Class 11

Answer 1

Right choice is (c) Iy = Ix + Iz

The explanation: The body is lying in the xz plane. The perpendicular axis theorem states that the moment of inertia of a planar body about an axis perpendicular to its plane is equal to the sum of moment of inertia about two perpendicular axes in the plane of the body. Iy is perpendicular to plane of body, so Iy = Ix + Iz.