On the discussion of hammer acceleration and let-off, Roger Waring
wrote "Despite the absence of direct human control at the point of
impact however, surely if you strike the key hard enough initially, you
can generate enough potential force to result in continued acceleration
beyond set-off."

Sorry Roger, but, as reported earlier, F = Ma.  If you remove the
force, it is impossible for any mass to continue accelerating.  No
acceleration means the velocity cannot increase.  In point of fact,
the velocity of the hammer must be decreasing (however slightly) due to
friction after let-off.  All this presupposes, of course, that the
hammer is not aided by gravity in its travel to the string.

If I could accelerate something without adding any force, I would be
a rich man, as perpetual motion machines are extremely rare in nature.

Ray Fairfield