In a closed system with no external forces, what happens to the total momentum?

• A. Momentum decreases over time
• B. Momentum is conserved only if speeds are equal
• C. Total momentum before equals total momentum after
• D. Momentum becomes zero after collision

Answer: (C)

Momentum is conserved in a closed system with no external forces. The total momentum of all objects remains the same before and after any interaction because the forces between them are internal. These internal forces pull on one object and push on another with equal strength in opposite directions, so the overall momentum of the group doesn’t change. This means the sum of all momenta initially equals the sum of all momenta after. It doesn’t require equal speeds, and it doesn’t automatically drop to zero—the total stays whatever it was to begin with, unless an external impulse changes it.