84. A thin uniform circular disc of mass M and radius R is rotating in a horizontal plane about an axis passing through its centre and perpendicular to its plane with an angular velocity ω . Another disc of same dimension but of mass M/4 is placed gently on the first disc coaxially. The angular velocity of the system now is
(a) 2ω/5
(b) 2ω/√5
(c) 4ω/5
(d) 4ω/√5
Ans. c
(14)