Question

If the sum of all external forces acting on a system is zero, then :

• A. Momentum of the system is constant
• B. Particles inside the system must be at rest
• C. System has no velocity
  
• D. None of the above

Answer 1

The correct option is A Momentum of the system is constant

If the resultant of all the external forces acting on a system of particles is zero, then from an inertial frame, one can surely say that:

1: Linear momentum of the system does not change in time.

2: Kinetic energy of the system does not change in time.
option A