In a one-dimensional collision between two particles, their relative velocity is `vec(v)_(1)` before the collision and `vec(v)_(2)` after the collision.

Options

A. `vec(v)_(1) = vec(v)_(2)` if the collision is elastic
B. `vec(v)_(1) =- vec(v)_(2)` if the collision is elastic
C. `|vec(v)_(2)| = |vec(v)_(1)|` in all cases
D. `vec(v)_(1) =- k vec(v)_(2)` in all cases, where `k ge 1`

Answer

B, C, D