Question

A force $\overrightarrow{F}=4\hat{i}-10\hat{j}$acts on a body at a points having position vector $-5\hat{i}$$-3\hat{j}$ relatives to origin of co-ordinates on the axis of rotation . The torque acting on body is

• A. $38\hat{k}$
• B. $-25\hat{k}$
• C. $62\hat{k}$
• D. None of these

Answer 1

Answer: (C)

$62\hat{k}$

$\begin{array}{c}\text{Given-* Force vector}\overrightarrow{F}=4\hat{i}-10\hat{j}\\ \ast \text{position vector}\overrightarrow{r}=-5\hat{i}-3\hat{j}\\ \text{we know that torque}\overrightarrow{\tau }-\\ \overrightarrow{\tau }=\overrightarrow{r}\times \overrightarrow{F}=(-5\hat{i}-3\hat{j})\times (4\hat{i}-10\hat{j})\\ \overrightarrow{\tau }=62\hat{k}\\ \text{Hence, (c) is the correct option.}\end{array}$