Physics - Rotation Question with Solution | TestHub

The angular momentum $\vec{L}$ of a particle about a point P is given by $\vec{L}=\vec{r}\times \vec{p}$, where $\vec{r}$ is the position vector from point P to the particle and $\vec{p}$ is its linear momentum.

If the point P is located on the line of motion of the particle, then the position vector $\vec{r}$ and the linear momentum vector $\vec{p}$ are parallel (or anti-parallel) to each other. The cross product of two parallel vectors is zero. Therefore, $\vec{L}=\vec{r}\times \vec{p}=0$. The angular momentum about point P is zero.