Q. Given $\overrightarrow{r} = 4\widehat{j}$ and $\overrightarrow{p} = 2\widehat{i} + 3\widehat{j} + \widehat{k}$. The angular momentum is
A) 4$\widehat{i} - 8\widehat{k}$
B) 8$\widehat{i} - 4\widehat{k}$
C) 8$\widehat{j}$
D) 9$\widehat{k}$
Explanation
(a) $\overrightarrow{L} = \overrightarrow{r} \times \overrightarrow{p} = \left| \widehat{\begin{array}{r}
i \\
0 \\
2
\end{array}}\ \ \ \ \ \widehat{\begin{array}{r}
j \\
4 \\
3
\end{array}}\ \ \ \ \widehat{\begin{array}{r}
k \\
0 \\
1
\end{array}} \right|$
$= \widehat{i}\lbrack 4 - 0\rbrack + \widehat{j}\lbrack 0 - 0\rbrack + \widehat{k}\lbrack 0 - 8\rbrack = 4\widehat{i} - 8\widehat{k}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.