Question

1. how do internal and external forces affect the law of conservation of momentum?

only internal forces can act on a system for the law of conservation of momentum to occur.
only external forces can act on a system for the law of conservation of momentum to occur.
external forces can act on a system, but the internal forces must double to counteract the external factors for the law of conservation of momentum to be observed.
both external and internal forces must be present for the law of conservation of momentum to occur.

Explanation:

According to the law of conservation of momentum, the total momentum of an isolated system remains constant. An isolated system is one where the net external force is zero. Internal forces are forces that act within the system (e.g., forces between parts of the system). External forces are forces that act on the system from outside (e.g., gravitational force from an external object). For the law of conservation of momentum to hold, the net external force on the system must be zero. However, internal forces can be present. But the question is about how internal and external forces affect the law. The law of conservation of momentum occurs when the net external force is zero. But internal forces are always there within the system (as long as there are parts in the system interacting). So, both internal and external forces are part of the system's scenario. The key is that for the law to be applicable (i.e., momentum is conserved), the net external force is zero, but internal forces are just forces within the system that don't contribute to a change in the total momentum of the system (because of Newton's third - law, internal forces come in action - reaction pairs and cancel each other out when considering the total momentum of the system).

Answer:

Both external and internal forces must be present for the law of conservation of momentum to occur.