Question

The net external torque on a system of particles about an axis is zero. Which of the following are compatible with it?

• A. The forces may be acting radially from a point on the axis
• B. The forces may be acting on the axis of rotation
• C. The forces may be acting parallel to the axis of rotation
• D. The torque caused by some forces may be equal and opposite to that caused by other forces

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A The forces may be acting radially from a point on the axis
B The forces may be acting on the axis of rotation
C The forces may be acting parallel to the axis of rotation
D The torque caused by some forces may be equal and opposite to that caused by other forces

When net external torque on a system of particles about an axis is zero,

$\overrightarrow{\tau }=\overrightarrow{r}\times \overrightarrow{F}$ = $rFsin\theta \overrightarrow{\tau }=0$

where,

$\theta$ is angle between $\overrightarrow{r}$, $\overrightarrow{F}$,$\overrightarrow{\tau }$

is unit vector along $\overrightarrow{\tau }$

.

them all the four statements (a),(b),(c ),(d) are compatible