Q: A metal piece of mass 120 g is stretched to form a plane rectangular sheet of area of cross section 0.54 m^{2}. If length and breadth of this sheet are in the ratio 1:6, find its moment of inertia about an axis passing through its centre and perpendicular to its plane.

Sol: Mass m = 120g = 120 × 10^{-3} kg

Area = lb = 0.54m^{2}

⇒ (b/6). b = 0.54 (∵l= b/6)

b^{2} = 0.54 × 6

⇒ $\large b = \sqrt{3.24} = 1.8 m $

$\large I = \frac{M(l^2 + b^2)}{12}$

I = 33.3 × 10^{-3} kg m^{2}