Two discs of same material and thickness have radii 0.2 m and 0.6 m. Their moments of inertia about their axes will be in the ratio

Options

(a) 1 : 81
(b) 1 : 27
(c) 1 : 9
(d) 1 : 3

Correct Answer:

1 : 81

Explanation:

I = (1/2) MR² = (1/2) (πR²t ρ) R² = πtρR⁴ / 2
t and p are same
I₁/I₂ = [R₁/R₂]⁴ = [0.2 / 0.6]⁴ = 1 / 81.