Question

A force $\overrightarrow{F}=\alpha \hat{i}+3\hat{j}+6\hat{k}$ is acting at a point $\overrightarrow{r}=2\hat{i}-6\hat{j}-12\hat{k}$. The value of $\alpha$ for which angular momentum about origin is conserved is

• A. 1
• B. -1
• C. 2
• D. 0.0

Answer 1

The correct option is B -1

For conservation of angular momentum about origin,
${\sum }^{}\overrightarrow{{\tau }_{net}}=0\Rightarrow \overrightarrow{r}\times \overrightarrow{F}=0\Rightarrow \alpha =-1$