Torque

Torque is the rotational analogue of force and is given by $\tau =rF\sin \theta$, where $r$ is the distance from the axis to the point of application and $\theta$ is the angle between the force and the position vector. Since the mechanic pushes perpendicular to the wrench, $\theta =90^{\circ }$ and $\sin \theta =1$, so the entire force is effective in turning the bolt. Then $\tau =(0.25\text{ m})(40\text{ N})(1)=10\text{ N m}$. The value 16 N m has no consistent physical origin and appears to mix unrelated numbers. The value 5 N m would result from halving the lever arm without any justification. The value 100 N m wrongly multiplies the force by 2.5 instead of 0.25, a place-value error. This is the direct NCERT definition of the moment of a force about a point, the quantity that produces angular acceleration. As a unit check, multiplying newtons by metres yields newton-metres, the correct dimension of torque, and the modest lever arm sensibly gives a modest turning effect of 10 N m.