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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
Angular momentum changes in direction but not in magnitude
Angular momentum changes both in direction and magnitude
Angular momentum is conserved
Angular momentum changes in magnitude but not in direction
Solution

The direction of $\vec{\omega}$ vector
is always $\perp^f$ to the plane
containing $\quad \overrightarrow{\mathrm{r}} \& \overrightarrow{\mathrm{v}}, \quad$ as
shown in fig. (at any instant).
Angular momentum
$\overrightarrow{\mathrm{L}}=\mathrm{I} \vec{\omega}$
Obviously, $\overrightarrow{\mathrm{L}}$ changes, as
$\vec{\omega}$ changes in direction but
$\overrightarrow \tau \Uparrow d\overrightarrow \theta $
$\therefore$ No work is done by torque due to weight of bob.
So $|\vec{\omega}|=$ constant
or $|\overrightarrow{\mathrm{L}}|=$ constant