Question

The position of a particle is given by $\overrightarrow{r}=(\hat{i}+2\hat{j}-\hat{k})$ and momentum $\overrightarrow{P}=(3\hat{i}+4\hat{j}-2\hat{k})$. The angular momentum is perpendicular to

• A. X-axis
• B. Y-axis
• C. Z-axis
• D. Line at equal angles to all the three axes

Answer 1

The correct option is A X-axis

Given,

$\overrightarrow{r}=\hat{i}+2\hat{j}-\hat{k}$

$\overrightarrow{P}=3\hat{i}+4\hat{j}-2\hat{k}$

Angular momentum, $\overrightarrow{L}=\overrightarrow{r}\times \overrightarrow{P}$

$\overrightarrow{L}=(\hat{i}+2\hat{j}-\hat{k})\times (3\hat{i}+4\hat{j}-2\hat{k})$

$\overrightarrow{L}=0\hat{i}-\hat{j}-2\hat{k}$

Hence, The angular momentum is perpendicular to the X-axis.

The correct option is A.