Angular Momentum Conservation

As stated in NCERT Class 11, Chapter 7 (System of Particles and Rotational Motion), when no external torque acts on a system its total angular momentum L = Iω is conserved. This conservation law is one of the most powerful tools in rotational dynamics because it links the body's mass distribution to its spin rate. The skater pulling in her arms is purely an internal rearrangement of mass, so the external torque about the vertical spin axis is essentially zero and angular momentum stays constant throughout the manoeuvre. Therefore we may write I₁ω₁ = I₂ω₂. Given that the new moment of inertia is I₂ = I₁/3, we solve ω₂ = (I₁/I₂)ω₁ = (I₁ / (I₁/3))ω₁ = 3ω₁, so the angular speed triples. The option 'Decreases to one-third' is wrong because reducing inertia must increase, not decrease, the spin rate. The option 'Remains unchanged' violates conservation of angular momentum whenever the moment of inertia changes. The option 'Increases to 9 times' incorrectly squares the inertia ratio, which would apply to energy, not angular speed. A consistency check confirms that since L is fixed, lowering I by a factor of three must raise ω by the same factor of three, matching the everyday observation of spinning skaters visibly speeding up as they draw their arms inward.