Which of the following best describes why momentum is conserved during a collision between two billiard balls on a frictionless table?

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Question

Which of the following best describes why momentum is conserved during a collision between two billiard balls on a frictionless table?

Accepted Answer

The net external force on the two-ball system is approximately zero — Momentum is conserved when the net external force on the system is zero (Newton's Second Law in impulse form: Δp = FΔt). On a frictionless table, no horizontal external forces act on the system. Option B misattributes conservation to material properties. Option C describes an elastic collision but is not the cause of momentum conservation. Option D incorrectly describes the forces as being in the same direction — they are equal and opposite.

Answer

The net external force on the two-ball system is approximately zero

Answer

The kinetic energy of both balls stays the same after the collision

Answer

The balls are made of a rigid material that stores no energy

Answer

Each ball exerts the same force in the same direction during impact

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