IN a headon collision between two particles, is it necessary that the particles will acquire a common velocity at least for one instant?

In an elastic collision between two particles

During inclined collision of two particle

Five particles are projected simultaneously from the top of a tower that is h = 32 m high. The initial velocities of projection are as shown in figure. Velocity of 2 and 5 are horizontal. (a) Which particle will hit the ground first? (b) Separation between which two particles is maximum at the instant the first particle hits the ground? (c) Which two particles are last and last but one to hit the ground? Calculate the distance between these two particles (still in air), at a time 0.3s after the third particle lands on ground. [g = 10 m//s^(2), tan 37^(@) = (3)/(4)]

In a one-dimensional collision between two particles, their relative velocity is vecv_(1) before the collision and vecv_(2) after the collision

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.

The relation between the particles velocity and wave velocity is -