A hot air ballon with a mass of 500kg ascends at a constant rate of 1.5 m/s for 20s. how much work is done by the upward force?

Work done = force * distance

Distance = speed * time; where speed = 1.5 m/s, and time = 20 s

distance = 30 m

Since the balloon is moving at a constant velocity, there is no net force acting on the balloon, the downwards force is equal to the upwards force. Thus, the downwards force is weight = upwards force = 500*9.8=4,900 N

Work done = 4,900*30 = 147,000 J