Question

The axis X and Z in the plane of a disc are mutually perpendicular and Y-axis is perpendicular to the plane of the disc. If the moment of inertia of the body about X and Y axes in respectively 30 kg $m^2$ and 100 $m^2$ then M.I about Z -axis in kg $m^2$ will be:-

• A. 70
• B. 50
• C. 10
• D. zero

Answer 1

The correct option is A 70

Moment of inertiar

$I_x=30kg{m}^2$ and $I_y=100kg{m}^2$

From perpendicular axis theorem,

$I_y=I_x+I_z$ from figure

$I_z=I_y-T_x$

$100-30=70kg{m}^2$