Question

Given $\overrightarrow{F}$ = (4$\hat{i}$ -10$\hat{j}$) and $\overrightarrow{r}$= (5$\hat{i}$-3$\hat{j}$). Then torque $\tau$ is

• A. -62$\hat{j}$
• B. 62$\hat{k}$
• C. 38$\hat{i}$
• D. 38$\hat{k}$

Answer 1

The correct option is D 38$\hat{k}$

$\tau =\overrightarrow{r}\times \overrightarrow{F}$

$=(5\hat{i}-3\hat{j})\times (4\hat{i}-10\hat{j})$

$=20(\hat{i}\times \hat{i})-12(\hat{i}\times \hat{j})-50(\hat{j}\times \hat{i})+30(\hat{j}\times \hat{j})$

$=0-12\hat{k}+50\hat{k}+0$

$=38\hat{k}$