How does one calculate inelastic collisions?

Hint :Collision, also called impact, in physics, the sudden, forceful coming together in direct contact of two bodies, such as, for instance, two billiard balls, a golf club and a ball, a hammer and a nail head, two railroad cars when being coupled together, or a falling object and a floor.

Complete Step By Step Answer:
An inelastic collision may be a collision during which there's a loss of K.E. While momentum of the system is conserved in an inelastic collision, K.E. isn't. This is often because some K.E. had been transferred to something else.
An inelastic collision is one during which the interior K.E. changes (it isn't conserved). This lack of conservation means the forces between colliding objects may remove or add internal K.E. Work done by internal forces may change the sorts of energy within a system.
Two objects that have equal masses head toward each other at equal speeds then stay together . Their total internal K.E. is initially 12mv2+12mv2=mv2 1 2 m v 2 + 1 2 m v 2 = m v 2. the 2 objects come to rest after sticking together, conserving momentum.

Note :
The difference between elastic & inelastic Collisions is that K.E. is conserved in Elastic collision, while K.E. isn't conserved in Inelastic collision. And, the Similarity with Elastic and non-elastic collision which, Momentum is conserved in both the cases.