A thin circular ring of mass M and radius R is rotating with a constant angular velocity 2   rad  …

A thin circular ring of mass M and radius R is rotating with a constant angular velocity 2 rad s-1 in a horizontal plane about an axis vertical to its plane and passing through the center of the ring. If two objects each of mass m be attached gently to the opposite ends of a diameter of ring, the ring will then rotate with an angular velocity (in rad s-1).
  1. MM+m
  2. M+2m2M
  3. 2MM+2m
  4. 2M+2mM

Solution

As the masses are gently placed we can apply conservation of angular momentum.

Initial moment of Inertia I1=MR2

Final moment of inertia I2=MR2+2mR2

By conservation of angular momentum

I1ω1=I2ω2MR2×2=M+2mR2×ω2

ω2=2MM+2m rad s-1

Asked in: JEE Main 2022 (26 Jun Shift 1)

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