In an elastic collision I. Energy is conserved II. Energy is decreased III. Energy is increased IV. Linear momentum conserved

Analyze the question: You are asked which statements are true about an elastic collision.

Concept:

• In an elastic collision, the total kinetic energy before the collision equals the total kinetic energy after it. Kinetic energy is conserved, so total energy is conserved too.
• In an inelastic collision, some kinetic energy is converted to heat, sound, or deformation, so kinetic energy decreases. (Total energy is still conserved, but not kinetic energy.)
• Linear momentum is conserved in all collisions (elastic and inelastic) as long as no external force acts on the system.

Evaluate each statement:

• I. Energy is conserved: TRUE. In an elastic collision, no kinetic energy is lost.
• II. Energy is decreased: FALSE. That describes an inelastic collision.
• III. Energy is increased: FALSE. A collision cannot create energy (except in explosions, which are not elastic collisions).
• IV. Linear momentum is conserved: TRUE. This is the principle of conservation of linear momentum.

So the true statements are I and IV only.

Answer: Option B.

Tip: Remember it this way: Momentum is always conserved in collisions. Kinetic energy is conserved only if the collision is elastic. When you see "elastic" in a JAMB question, think "both energy and momentum conserved."