aside to Dr. Uretsky,
I suppose that my initial question was borne out of the wording of the problem as posed by the source..."perfectly elastic" and exact recoil speed...etc. I am aware that the more massive the wall, the less it moves and the closer the recoil speed approaches the initial speed...in other words, the essential physics comes out of an understanding of the limiting cases of the quantities involved. I suppose that I was quibbling with the statement of the situation (which I did not describe in detail).