Question

A disc of mass m0 rotates freely about a fixed horizontal axis passing through its centre. A thin cotton pad is fixed to its rim, which can absorb water. The mass of water dripping onto the pad per unit time is μ. After what time will the angular velocity of the disc get reduced to half its initial value?

(a) 2m0/μ

(b) 3m0/μ

(c) m0/μ

(d) m0/2μ

Answer 1

Correct Answer is: (d) m0/2μ

L = I0ω0 = Iω0/2

or 2I0 = I

or 2(1/2 m0r2) = 1/2 m0r2 + (μt)r2

or t = m0/2μ