Two objects interact with each other and with no other objects. Initially object A has a speed of 5 m/s and object B has a speed of 10 m/s. In the course of their motion they return to their initial positions. Then A has a speed of 4 m/s and B has a speed of 7 m/s. We can conclude

We can conclude that there is a decrease in kinetic energy of the particles due to their elastic collision, since kinetic energy is directly proportional to squared velocity of the particles.

Explanation:

Given:

initial velocity of particle A, Ua = 5m/s

initial velocity of particle B, Ub = 10 m/s

final velocity of particle A, Va = 4m/s

final velocity of particle B, Vb = 7m/s

For particle A:

The final velocity is 1 less than the initial velocity.

For particle B:

The final velocity is 3 less than the initial velocity.

We can conclude that there is a loss in kinetic energy due to elastic collision of the two particles, since kinetic energy is directly proportional to squared velocity of the particles. A decrease in velocity means decrease in kinetic energy.