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If mechanical work is defined as equal to a force times the applied
distance, and since forces are supposed to always occur in pairs, work
might always be considered as being done by opposing the matching
force that's against it.
As for applying that to an ambiguous case, consider:
a) a person lifts a weight in a stationary elevator 5 ft.
b) the elevator rises 5 ft and the person holds the weight against their
waist. The person applied force against the weight while it rose.
(They applied a force over a distance, right?)
c) the person "lifts" the weight 5ft while the elevator actually goes
down 5ft. The weight's actual altitude thusly did not change. A
camcorder fixed in the elevator would show the same view in a) or c).
In which case(s), a,b, & c, was work actually done and by whom or
what? Have you ever considered this situation or something equivalent?