hi jimi70

Cannot find the error at the moment but I'll keep working on it.

It's not too bad to work with algebra throughout though:

and after the wall impact

Express all in terms of u_a

Let D be the distance from the wall for second impact

Back later when I've found some more paper to work this out.

A LITTLE LATER:

Curious. I'm getting

which agrees with your numeric version.

Bob