A uniform ring rotates about the vertical axis shown with initial angular speed ω. An insect of the same mass as the ring walks from P₁ to P₂. If no external torque acts about the axis, what is the final angular speed of the ring?

Question

G1 Physics · Accepted Answer

No external torque acts about the vertical axis, so angular momentum is conserved. Initially L=I of ring × ω=MR²ω. After the insect of equal mass reaches P₂, use the new total moment of inertia about the same axis and set initial angular momentum = final angular momentum. For the geometry shown this gives final angular speed ω/3. Hence option B.