Momentum and Kinetic energy are conserved in

Analyze the question: We need the type of event in which both momentum and kinetic energy are conserved.

Explain the concept:

• Momentum is conserved in all collisions and explosions, provided no external force acts on the system.
• Kinetic energy is conserved only in a special kind of collision called a perfectly elastic collision.

Check each option:

• A. Inelastic collision: Momentum is conserved, but some kinetic energy is changed into heat, sound or deformation. Kinetic energy is not conserved. ❌
• B. Elastic collision: Both total momentum and total kinetic energy are conserved. Examples are collisions between gas molecules and between ideal billiard balls. ✅
• C. Explosion: Momentum is conserved, but kinetic energy increases because chemical or stored energy is released. ❌
• D. Spacecraft: This is not a type of collision. A spacecraft moving by rocket propulsion conserves momentum, but kinetic energy changes as fuel burns. ❌

Answer: The correct option is B. Elastic collision.

Tip: Remember that momentum is always conserved in an isolated system, but kinetic energy is conserved only in elastic collisions. If a question says "both are conserved," think "elastic."