Question

Find the torque $(\overrightarrow{\tau }=\overrightarrow{r}\times \overrightarrow{F})$ of a force $\overrightarrow{F}=-3\hat{j}+5\hat{k}$ acting at the point $\overrightarrow{r}=7\hat{i}+3\hat{j}+\hat{k}$.

• A. $-14\hat{i}+38\hat{j}+16\hat{k}$
• B. $4\hat{i}+4\hat{j}+6\hat{k}$
• C. $-14\hat{i}+38\hat{j}-16\hat{k}$
• D. $18\hat{i}-35\hat{j}-21\hat{k}$

Answer 1

The correct option is D $18\hat{i}-35\hat{j}-21\hat{k}$

$\overrightarrow{\tau }=\overrightarrow{r}\times \overrightarrow{F}=(7\hat{i}+3\hat{j}+\hat{k})\times (-3\hat{j}+5\hat{k})$

$\overrightarrow{\tau }=18\hat{i}-35\hat{j}-21\hat{k}$

Torque is $18\hat{i}-35\hat{j}-21\hat{k}$