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 amay 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

Correct Answer - A::B::C::D
When net external torque on a system of particles about an axis is zero, i.e.., `overset rarr(tau) = overset rarr(r ) xx overset rarr(F) = r F sin theta hat tau = Zero`, where, `theta` is angle between `overset rarr(r ) and overset rarr(F), hat tau` is unit vector along `overset rarr(tau)`, them all the four statements (a),(b),(c ),(d) are compatible.