When two bodies stick together after collision, the collision is said to be
A. Partially elastic
B. Elastic
C. Inelastic
D. Perfectly inelastic

Hint: Recall the change in momentum and kinetic energy of the colliding bodies before and after collision for all given options. If the colliding objects stick together after collision, the greatest portion of energy is lost in the collision.

Complete step by step answer:
Let’s verify each option as follows,

Partially elastic

Practically, all the collisions we see are partially inelastic collisions or partially elastic collisions. In partially inelastic collisions, some of the kinetic energy or momentum is lost after the collision. But theoretically, we assume only elastic collisions and inelastic collisions.

Therefore, the option (A) is incorrect.

Elastic

In elastic collisions, the kinetic energy and momentum of the system remains conserved. In elastic collision, the colliding objects bounce apart and do not stick together.

Therefore, the option (B) is incorrect.

Inelastic

In inelastic collision or partially inelastic collision, some of the energy is lost in the collision but the colliding objects do not stick together after collision.

Therefore, the option (C) is incorrect.

Perfectly inelastic

In a perfectly inelastic collision, we can say all the energy lost in the collision and the colliding objects sticks together after the collision. The real-life example of perfectly inelastic collision is when we strike the football towards the wall and the football sticks to the wall.

So, the correct answer is option (D).

Note: To answer such questions, students should notice if the option of perfectly inelastic collision is given or not. In inelastic collisions, the colliding objects do not necessarily stick together. The final velocity of the system can be calculated if the initial velocity of the colliding bodies is given for the perfectly inelastic collision.