Question

A bob of mass m attached to an inextensible string of length l is suspended from a vertical support. The bob rotates in a horizontal circle with an angular speed $\omega rad/S$ about the vertical. About the point of suspension,

• A. angular momentum changes in direction but not in magnitude.
• B. angular momentumchanges both in direction and in magnitude.
• C. angular momentum is conserved.
• D. angular momentum changes in magnitude but not in direction.

Answer 1

The correct option is A angular momentum changes in direction but not in magnitude.

Torque of weight about point of suspension. ${\tau }_{weight}=mg\times lsin\theta$
Direction of torque by weight is parallel to the plane of rotation of the particle.

As $\overrightarrow{\tau }$ is perpendicular to the angular momentum of the bob so the magnitude of angular momentum remains the same but direction changes.