Originally Posted by sureshs
There is nothing wrong, but there is nothing useful either. If you remember all the collision problems you have solved, do you ever recall any mention of acceleration? No, it was always, u1, v1, u2, v2 etc. Why? Because no force was acting on those objects. When a racket head hits a ball, it is accelerating just prior to impact. So, conservation of momentum cannot be applied.
I understand, and you are right in the large picture. But we are applying the rules differentially, as when solving a problem in numerical analysis, by dividing time into very small segments.