Conservation in Elastic Collisions

Steps:

• Identify collision type: Elastic means kinetic energy is conserved by definition.
• Check external forces: None present, so total linear momentum is conserved via Newton's laws.
• Apply conservation laws: Momentum conservation holds for isolated systems; elastic adds kinetic energy conservation.
• Match to options: Both conserved, so select A.

Why A is correct:

• Elastic collisions conserve both total momentum (no external forces) and total kinetic energy (defining feature, via coefficient of restitution = 1).

Why the others are wrong:

• B describes inelastic collisions, where kinetic energy converts to other forms.
• C violates momentum conservation in isolated systems.
• D applies only if external forces act or collision is non-isolated/non-elastic.

Final answer: A