Solo Lupus 50
Talking about gliders seems a red herring in this discussion.
From the original, the question has to do with accelerating a reduction in velocity. It is a Rate question, and demands a little latitude in parameters.
So my assumption was from the beginning that the engines on both slowing a/c were 'mass only', not thrust. We could get into "windmilling" v. Flight idle, but as we see with seven pages, most here are not satisfied unless the discussion can be made more complex, not less.
To some extent it is a "Straw Thread", a vehicle for trotting out some algebra in the interest of appearing cerebrally massive.