Final answer:
The kinetic energy lost in a completely inelastic collision can be determined by calculating the difference in the total internal kinetic energy of the system before and after the collision, which turns into thermal energy and sound.
Step-by-step explanation:
When two particles collide completely inelastically, kinetic energy is lost during the collision. This loss is due to the kinetic energy being converted into other forms of energy such as thermal energy and sound. To quantify the kinetic energy lost, one would first calculate the total internal kinetic energy of the system before the collision and then again after the collision. The difference between these two values would give the amount of kinetic energy that has been dissipated. The laws of conservation of momentum can aid in determining the final velocities of the colliding objects, which are needed to find the kinetic energy after the collision. In perfectly inelastic collisions, the objects stick together and move with the same final velocity, making the calculation more straightforward.