The net value of an external torque acting on a system of particle is zero about a certain axis of rotation. Which of the following statements will hold good for the system?
(a) The forces may be acting radially from a point on the axis
(b) The forces may be directed along the axis of rotation
(c ) The forces may be acting parallel to the axis of rotation
(d) The torques caused by some forces are equal and opposite to those caused by other forces.

Options

A. (i) only
B. (i) and (ii)
C. (i), (ii), (iii)
D. All of these

Answer

D

Explanation

Since the external torque on the system of particles is zero, there will be neither rotation nor translatory motion of the particles. All the four conditions for the forces acting must hold good in order to make the external torque zero.