When does the magnitude of angular momentum become zero?

$A$ particle of mass $m$ is moving with constant velocity $v$ parallel to the $x$-axis as shown in the figure. Its angular momentum about origin $O$ is ..........

As shown in the figure,a particle of mass $m$ moves with a velocity $v$ along the line $PC$. What is the angular momentum of this particle with respect to point $P$?

The diameter of a flywheel is $1 \,m$. It has a mass of $20 \,kg$. It is rotating about its axis with a speed of $120$ rotations in one minute. Its angular momentum in $kg-m^2/s$ is (in $4$)

Define angular momentum.

$A$ particle of mass $m$ is moving in time $t$ on a trajectory given by $\overrightarrow{r} = 10 \alpha t^2 \hat{i} + 5 \beta (t - 5) \hat{j}$. Where $\alpha$ and $\beta$ are dimensional constants. The angular momentum of the particle becomes the same as it was for $t = 0$ at time $t = \dots$ seconds.