JEE Main 2024 Physics question
A thin 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 angular velocity ω. If another disc of same dimensions but of mass is placed gently on the first disc co-axially, then the new angular velocity of the system is:
Answer: (C)
Solution
Angular momentum is conserved: ½MR²ω = (½MR² + ½(M/2)R²)ω′ = (3/4)MR²ω′ ⇒ ω′ = 2ω/3.