A perfectly elastic collision is a collision: a. Between two springs. b. That conserves thermal energy. c. That conserves kinetic energy. d. That conserves potential energy. e. That conserves mechanical energy.

Answer: c)

Explanation:

By definition, a perfectly elastic collision is one where the kinetic energy of the system composed by the bodies colliding, is the same, before and after collision.

If the system is composed of a mass m₁, with an initial velocity v₁₁, and a mass m₂, with an initial velocity v₂₁, after the collision, m₁ will have a velocity v₁₂, and m₂, a velocity v₂₂.

if the collision is perfectly elastic, the following equation must be true:

1/2 m₁ v₁₁² + 1/2 m₂ v₁₂² = 1/2 m₁ v₁₂² + 1/2 m₂ v₂₂²

As in any collision, momentum must be conserved also.