What does the principle of conservation of momentum entail?

• A. Momentum is irrelevant in closed systems
• B. The total momentum of a system remains constant if no external forces act
• C. Momentum increases with velocity
• D. Momentum is always lost after collisions

Answer: (B)

The principle of conservation of momentum states that the total momentum of a closed system remains constant if no external forces act upon it. This means that in an isolated system, where no net external force is influencing the movement of the objects within that system, the momentum before an interaction, such as a collision, will be equal to the momentum after the interaction.

Momentum is defined as the product of an object's mass and its velocity. Since no external forces are acting, the internal forces that objects exert on each other during collisions or interactions will not change the overall momentum of the system. This concept is fundamental in physics, particularly in analyzing collisions and the behavior of objects in isolated systems.

The other choices do not correctly capture the essence of the principle. In particular, the notion that momentum is irrelevant in closed systems or that it always decreases after collisions contradicts the foundational understanding of how momentum operates in such scenarios.