Question

A force of $-f\hat{k}$ acts on $O$, the origin of the co-ordinate system. The torque about the point $(1,-1)$ is

• A. $F(\hat{i}-\hat{j})$
• B. $-F(\hat{i}+\hat{j})$
• C. $F(\hat{i}+\hat{j})$
• D. $-F(\hat{i}-\hat{j})$

Answer 1

The correct option is B $-F(\hat{i}+\hat{j})$

We know torque$\overrightarrow{\tau }=(\hat{i},-\hat{j})\times -f\hat{k}$

$\overrightarrow{\tau }=-f(\hat{i}+\hat{j})$