Question

With reference to figure of a cube of edge a and mass m, which of the following is the incorrect statement?

(O is the centre of the cube)

• A. The moment of inertia of cube about z’ is
• B. The moment of inertia of cube about z”is
• C. Ix=Iy
• D. None of these

Answer 1

Answer: (B)

The moment of inertia of cube about z”is

Answer 2

As z axis is parallel to z’ axis and distance between them

By the theorem of parallel axes,

$I _ { z } ^ { \prime } = I _ { z } + m \left( \frac { a } { \sqrt { 2 } } \right) ^ { 2 } = I _ { z } + \frac { m ^ { 2 } } { 2 }$

Hence, option (1) is correct.

z and z” are notj parallel axes. Hence, option (2) is incorrect.

By symmetry, hence, option (3) is correct