Momentum of a system is conserved only when question 16 options: there are no internal forces acting on the system. the system is not moving. there are no forces acting on the system. there is no net external force acting on the system. the system has zero momentum.

Like mass and energy, it is already part of the natural phenomena that momentum is always conserved. However, just like energy, there are exception to this rule. This is when an external force is applied to the system which causes it to work reversely. Therefore, momentum is conserved when no net external force is applied.