Q: Four thin rods of same mass M and same length l, form a square as shown in figure. Moment of inertia of this system about as axis through centre O and perpendicular to its plane is
(a) $\frac{4}{3} m l^2 $
(b) $\frac{1}{3} m l^2 $
(c) $\frac{1}{6} m l^2 $
(d) $\frac{2}{3} m l^2 $
Ans: (a)