Which type of force can act through empty space?
here, i hope this .
correct answer is positive force → balanced force → negative force
when diego gives a big lift to the piano with the of pulley system that time, initially piano moves upward so positive force acts on it.
later, piano stops, in this condition balanced force act on it since force applied by diego is balanced by gravitational force of earth.
after some time piano starts falling in this condition negative force will act on the piano. in this condition, gravitational force will acts on piano in downward direction.
(b) would be the logical answer because that would be the only graph that means that the speed is increasing as time passes.