JEE Main 2024 Physics question
Two discs of moment of inertia I₁ = 4 kg m² and I₂ = 2 kg m², about their central axes and normal to their planes, rotating with angular speeds 10 rad/s and 4 rad/s respectively are brought into contact face to face with their axes of rotation coincident. The loss in kinetic energy of the system in the process is J.
Answer: 24
Solution
By conservation of angular momentum, 4 × 10 + 2 × 4 = 6ω, so ω = 8 rad/s. Loss in KE = ½[4 × 100 + 2 × 16 − 6 × 64] = ½ × 48 = 24 J.