decelerate. The velocity of the front block A (which was slower initially) will gradually increase, and the velocity of the rear block B (which was faster initially) will gradually decrease. The spring will continue to become more and more compressed as long as the rear block B is faster than the front block A. There will be an instant t1+ Δt when the two blocks will have equal velocities. At this instant, both the ends of the spring will move with the same velocity and no further compression will take place. This corresponds to the maximum compression of the spring. Thus, "the spring-compression is maximum when the two blocks attain equal velocities".
As the spring is compressed it tries to regain its shape in a way pushes the two block so block A is accelerated and B is decelerated the elastic potential energy stored in spring is converted back into kinetic energy of the block. In the whole process as there is no external force acting on the system the initial and final momentum is conserved. And inial and final kinetic energy is same as thee is no loss in the spring elastic energy it is wholly converted to the kinetic energy.
The same model can be used for the collision of rigid bodies if there is no plastic deformation then the collision is elastic and kinetic energy before and after the collision remains the same.
It is a ratio of the velocity of approach of two colliding bodies to the velocity of separation.
IN PERFECTLY ELASTIC COLLISION THE KINETIC ENERGY AFTER AND BEFORE THE COLLISION IS SAME BUT IT IS INCORRECT TO SAY THAT IT IS CONSTANT .
IN COLLISION BETWEEN TWO BODIES AS SYSTEM IN ABSENCE OF EXTERNAL FORCE ,MOMENTUM IS CONSERVED.
IN CASE OF INCLINED COLLISION ALWAYS WRITE THE EQATION OF MOMENTUM ALONG THE LINE PERPENDICULAR TO THE LINE OF IMPACT AS THE NORMAL FORCE, DURING COLLISION ACTS AS AN EXTERNAL FORCE.