A child standing on the edge of a freely spinning merry-go-round moves quickly t

Question

A child standing on the edge of a freely spinning merry-go-round moves quickly to the center. Which one of the following statements is necessarily true concerning this event and why?
a. the angular speed of the system increases because the moment of inertia of the system has decreased.
b. the angular speed of the system increases because the moment of inertia of the system has increased.
c. The angular speed of the system decreases because the moment of inertia of the system has increased.
d. The angular speed of the system remains the same because the net torque on the merry-go-round is zero N x m.
e. The angular speed of the system decreases because the moment of inertia of the system has decreased.

Explanation / Answer

As the child moves to the center of the merry-go-round, the moment of inertia of the system decreases because it's mass becomes distributed more towards the center of its axis of rotation. The child moving to the center of the merry-go-round has essentially the same effect as an ice skater pulling their arms in during a spin. Thus, the angular velocity of the merry-go-round increases.

Answer: A

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