Question

As you finish listening to your favorite compact disc (CD), the CD in the player slows down to a stop. Assume that the CD spins down with a constant angular acceleration. What is the reason for the CD slowing down?

1) Friction between the CD and the player
2) Decrease in the applied torque
3) Increase in the rotational inertia of the CD
4) Conservation of angular momentum

Answer 1

The CD slows down because of the increase in rotational inertia and conservation of angular momentum.

Step-by-step explanation:

The reason for the CD slowing down is increase in the rotational inertia of the CD (option 3) and conservation of angular momentum (option 4).

As the CD slows down, its rotational inertia increases because the mass of the CD is distributed farther from the center, causing a resistance to the rotational motion. This increase in rotational inertia is a result of external forces acting on the CD, such as friction between the CD and the player, which opposes the spinning motion.

Additionally, the CD slows down due to conservation of angular momentum. Angular momentum is conserved in a closed system, meaning that the initial angular momentum of the CD should be equal to the final angular momentum. As the CD slows down, its angular velocity decreases, and to maintain the conservation of angular momentum, the rotational inertia must increase.