If two cars collide, they usually do not stick. This does not mean that the collision is elastic.
Explanation:
A collide is defined as an encounter or interaction of particles or objects that causes an exchange of energy and / or amount of movement.
In an elastic collision, the total kinetic energy is conserved. That is, the total kinetic energy of all objects in the system after the collision is equal to their total kinetic energy before the collision. Kinetic energy could be exchanged between system objects; but the total kinetic energy of the system will remain constant.
Rigid billiard ball crashes are an example of an elastic collision. When the balls collide frontally if one of the balls is at rest, after the collision the thrown ball is at rest while the other ball moves with a speed equal to the first.
In an inelastic collision, total kinetic energy is not conserved. This means that part of the kinetic energy is changed in some other form of energy in the collision. In this way, for example, one or more of the objects that collide may not recover their original form. For example, a rubber ball that bounces against a wall or floor. The ball deforms when it hits the surface. Permanently deforming an object requires work, and that work is done at the expense of the original kinetic energy of the system. Then it is said that there are collisions in which part of the energy in deforming is dissipated.
When two objects collide and after the collision are joined, the shock is called totally inelastic. For example, two plasticine masses that collide and stay together, moving as one piece after the crash.
If two cars collide, they usually do not stick. This does not mean that the collision is elastic. If the total kinetic energy of all objects in the system after the collision is equal to its total kinetic energy before the collision. That is, both retain the same kinetic energy and thus speed. But it may happen that total kinetic energy is not conserved. In this way, for example, a deformation occurs when the impact occurs. So, unless the problem indicates that it is a completely elastic collision, it cannot be assumed that it is.
