Question

Figure shows two forces each of magnitude $10N$ acting at the points $A$ and $B$ at a separation of $50cm$, in opposite directions. Calculate the resultant moment of the two forces about the point $O$, situated exactly at the middle of two forces :

• A. $500N$ $m$ anti clockwise
• B. $500N$ $m$ clockwise
• C. $5N$ $m$ clockwise
• D. $5N$ $m$ anti clockwise

Answer 1

The correct option is C $5N$ $m$ clockwise

Moment for force acting on point $A$$=\overrightarrow{r}\times \overrightarrow{F}=(-50/200(\hat{i}\left)\right)\left(10\right(\hat{j}\left)\right)=2.5\widehat{(-k)}Nm$

Moment for force acting on point $B$$=\overrightarrow{r}\times \overrightarrow{F}=\left(50/200\right(\hat{i}\left)\right)\left(10\right(-\hat{j}\left)\right)=2.5\widehat{(-k)}Nm$

So, total moment about point '$O$'=$5\widehat{(-k)}Nm$

Now applying right hand thumb rule we can say that moment will be clockwise