Originally Posted by bhupaes
I believe the objective is to model the collision in a very small timeframe that brackets the collision. How the racquet and ball achieved their speeds and direction would be immaterial for the purposes of this exercise. I believe this is what toly is trying to do, in order to simplify the model/calculations used, and I don't see anything wrong with it...
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.