Question

when an aeroplane takes off the work done by its weight is

Answer 1

well the work being done is against gravity,gravity is thus doing negative work on it.and work done by plane by its internal forces will be 'mgh'

Answer 2

Work done =integration of force and displacement.
W =FScos(angle between the force and displacement)
as Work done does not depends on mass or weight...its ans will be zero