A figure skater begins a spin with her arms stretched outward
PHYSICS · Single correct · CBSE · Physics · System of Particles and Rotational Motion · System of Particles and Rotational Motion
Problem
A figure skater begins a spin with her arms stretched outward. She then pulls her arms in close to her body, decreasing her moment of inertia about the spin axis. Which of the following best explains why her angular speed increases even though she experiences no noticeable external torque?
(a) Decreasing her moment of inertia reduces friction with the air, allowing her to spin faster.
(b) Her total mechanical energy must remain constant; therefore when her moment of inertia decreases her angular speed increases to keep the rotational kinetic energy unchanged.
(c) Her angular momentum remains constant, so a decrease in moment of inertia must be accompanied by an increase in angular speed.
(d) Internal forces within her body exert a net external torque on her, causing her angular speed to increase.