Question

If the line of action of the applied force intersects the Axis of rotation, then the torque of this force about the axis of rotation is

• A. Always zero
• B. Always non-zero perpendicular to the axis of rotation
• C. Sometime non-zero
• D. Non-zero and along the axis of rotation

Answer 1

The correct option is A

Always zero

Torque of force $\overrightarrow{F}$ can be mathematically stated as,

$\overrightarrow{T}$ = $\overrightarrow{r}$ $x$ $\overrightarrow{F}$ Hence, if line of action of force intersects the Axis of rotation at point O then consider your origin to be at O and $|\overrightarrow{T}|$ = 0

So it will be zero about any point considered on Axis of rotation. i.e., It will have no turning effect upon the body about the axis of rotation.