You are sitting on a stool that can rotate friction-free about its vertical axis, holding a mass in each outstretched hand. When you suddenly release and drop the masses, your angular velocity
A) increases.
B) stays the same.
C) decreases.
D) becomes zero.

Question

Quizplus · Accepted Answer

When you release the masses, the external torque acting on the system (you and the stool) is zero. According to the conservation of angular momentum, if no external torque is applied, the angular momentum of a system remains constant. Since angular momentum is the product of moment of inertia and angular velocity, and your moment of inertia decreases when you release the masses (as they are no longer part of the system), one might expect your angular velocity to change to conserve angular momentum. However, the question specifies that the masses are dropped, not thrown, meaning they do not impart any additional angular momentum to the system upon release. Therefore, your angular velocity remains unchanged.

You Are Sitting on a Stool That Can Rotate Friction-Free