Question

Two rods each of mass m and lenght l are joined at the centre to form a cross. The moment of inertia of this cross about an axis passing through the common centre fo the rods and perpendicular to the plane formed by them, is:

• A. ml2/12
• B. ml2/6
• C. ml2/3
• D. ml2/2.

Answer 1

Answer: (B)

ml2/6

Answer 2

Moment of inertia of system about Z-axis

$= I _ { A B } + I _ { C D }$ $= \frac { m l ^ { 2 } } { 12 } + \frac { m l ^ { 2 } } { 12 } = \frac { m l ^ { 2 } } { 6 }$