Collisions

What is a Perfectly Elastic Collision (Elastic Collision)?

Total momentum AND total kinetic energy of the system are the same before and after the collision.

What happens to Kinetic Energy during a Perfectly Elastic Collision?

KE lost by one body is entirely transferred to the other; total KE remains constant before and after. Internal energy changes (potential energy) during impact are fully reversible.

What is the relative speed of approach in a perfectly elastic collision?

Equal to the relative speed of separation (u₁ - u₂ = v₂ - v₁ for 1D).

What is an Inelastic Collision?

Total momentum of the system is conserved, but total kinetic energy after collision is LESS than before.

What happens to Kinetic Energy during an Inelastic Collision?

Some KE is converted into other forms (sound energy, internal energy due to deformation). Total KE decreases.

What is a Completely Inelastic Collision?

An inelastic collision where bodies stick together (coalesce) after impact, moving with the same final velocity. Total momentum is conserved, but total KE is not.

What is the Problem-Solving Technique for Solving Collision Problems?

First, identify the type of collision. Then, apply the relevant laws (Conservation of Momentum, and KE conservation for elastic collisions, or same final velocity for completely inelastic).

When using velocity signs in equations?

Choose a positive direction (e.g., right); include a negative sign for numerical substitution if a body moves in the opposite direction.