Question

Calculate total moment of the two forces about $O$.

• A. $2N$ $m$(clockwise).
• B. $2N$ $m$(anti clockwise).
• C. $4N$ $m$(clockwise).
• D. $4N$ $m$(anti clockwise).

Answer 1

The correct option is A $2N$ $m$(clockwise).

Net torque $=\Sigma r\times F$

The rod is pivoted at O, and A and B are at a distance of $2m$ and $4m$ respectively.

$5N$ of force is applied at point A, thus torque produced is,

${\tau }_A=5\times 2=10Nm$ in the anti-clockwise direction.

$3N$ of force is applied at point B creating a torque,

${\tau }_B=3\times 4=12Nm$ in the clockwise direction.

Thus net torque on the system is $\tau ={\tau }_A+{\tau }_B$

$\tau =2Nm$ in the clockwise direction.