Question

A force $\overrightarrow{F}=3\hat{i}+4\hat{j}-3\hat{k}$ is applied at the point $P$, whose position vector is $\overrightarrow{r}=2\hat{i}-2\hat{j}-3\hat{k}$. What is the magnitude of the moment of the force about the origin?

• A. $23units$
• B. $19units$
• C. $18units$
• D. $21units$

Answer 1

Answer: (A)

$23units$

$\overrightarrow{M}=\overrightarrow{r}\times \overrightarrow{F}=18\hat{i}-3\hat{j}+14\hat{k}$

$\therefore |\overrightarrow{M}|=\sqrt{{18}^2+3^2+{14}^2}=\sqrt{529}=23$ units.

This is the required solution.