Question:
The net external torque on a system of particle about any 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
Solution:
The correct is all the four options