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 rad/s about the vertical. About the point of suspension :
angular momentum is conserved.
angular momentum changes in magnitude but not in direction.
angular momentum changes in direction but not in magnitude.
angular momentum changes both in direction and magnitude.
As we have learned
Angular momentum -
- wherein
represent angular momentum of a moving particle about a point.
it can be calculated as
= Length of perpendicular on line of motion
= component of momentum along perpendicualar to

Angular momentum = mvr is constant as distance of bob from point of suspensions and its speed both are constant.
Direction of angular momentum changes continually as shown in figure
Option 1)
angular momentum is conserved.
Option 2)
angular momentum changes in magnitude but not in direction.
Option 3)
angular momentum changes in direction but not in magnitude.
Option 4)
angular momentum changes both in direction and magnitude.
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