In a closed system, which statement best describes momentum during a collision?

In a closed system, which statement best describes momentum during a collision?

• A. Momentum increases after collision.
• B. Momentum is conserved in a closed system.
• C. Momentum decreases because energy is lost.
• D. Momentum is redistributed unpredictably.

Answer: (B)

Momentum is conserved in a closed system during a collision. When there are no external forces acting on the system, there’s no external impulse to change the total momentum, so the vector sum of the momenta of all objects remains the same before and after the collision. The forces between the colliding bodies are internal, so they can swap momentum between the objects, but the overall amount doesn’t change. This is true even if some energy is transformed into heat, sound, or deformation; the momentum balance still holds because energy can change forms while momentum stays constant. The other ideas imply a change in the total momentum or rely on energy loss to explain momentum, which isn’t accurate. Momentum doesn’t have to increase after a collision, and it isn’t redistributed in a way that’s inherently unpredictable—the internal interactions simply shuffle how momentum is shared while keeping the total fixed.

Momentum is conserved in a closed system during a collision. When there are no external forces acting on the system, there’s no external impulse to change the total momentum, so the vector sum of the momenta of all objects remains the same before and after the collision. The forces between the colliding bodies are internal, so they can swap momentum between the objects, but the overall amount doesn’t change. This is true even if some energy is transformed into heat, sound, or deformation; the momentum balance still holds because energy can change forms while momentum stays constant.

The other ideas imply a change in the total momentum or rely on energy loss to explain momentum, which isn’t accurate. Momentum doesn’t have to increase after a collision, and it isn’t redistributed in a way that’s inherently unpredictable—the internal interactions simply shuffle how momentum is shared while keeping the total fixed.