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A mass m tied to a light inextensible string of length l hangs from a fixed point. The mass moves in a horizontal circle with angular speed ω about the vertical line through the point of suspension. With respect to the point of suspension, which statement is true about its angular momentum?

1. It remains conserved.
2. Its magnitude varies, but its direction stays fixed.
3. Its direction changes, but its magnitude remains constant.
4. Both its direction and magnitude keep changing.

Correct answer: Its direction changes, but its magnitude remains constant.

Solution

The angular momentum of the mass remains constant in magnitude because the speed and distance from the axis of rotation do not change, but its direction changes continuously as the mass moves in a circular path.

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