Question

The moment of the force, $\overrightarrow{F}=4\hat{i}+5\hat{j}-6\hat{k}$ at $(2,0,-3)$, about the point $(2,-2,-2)$ is given by.

• A. $-7\hat{i}-8\hat{j}-4\hat{k}$
• B. $-8\hat{i}-4\hat{j}-7\hat{k}$
• C. $-7\hat{i}-4\hat{j}-8\hat{k}$
• D. $-4\hat{i}-\hat{j}-8\hat{k}$

Answer 1

Answer: (C)

$-7\hat{i}-4\hat{j}-8\hat{k}$

where, $\overrightarrow{r}=2\hat{j}-\hat{k}$

Moment of force = $\overrightarrow{r}\times \overrightarrow{F}$

$=[2\hat{j}-\hat{k}]\times [4\hat{i}+5\hat{j}-6\hat{k}]$

= $-7\hat{i}-4\hat{j}-8\hat{k}$