Question

A mass m is moving with a constant velocity along a line parallel to the x-axis, away from the origin. Its angular moment with respect to the origin

• A. Is zero
• B. Remains constant
• C. Goes on increasing
• D. Goes on decreasing

Answer 1

Answer: (B)

Angular momentum of the particle about origin O will be given by

$\overrightarrow{L}=\overrightarrow{r}\times \overrightarrow{p}=\text{m}\left(\overrightarrow{r}\times \overrightarrow{V}\right)$
$\text{or}\left|\overrightarrow{L}\right|=\text{L}=\text{mrV sin}\theta$
$=\text{mV}\left(\text{r sin}\theta \right)=\text{mVh}$
Now, $\text{m,V}$ and $\text{h}$ all are constant
Therefore, angular momentum of particle about origin will remain constant. The direction of $\overrightarrow{r}\times \overrightarrow{v}$ also remains the same (negative z direction)