On a perfect day, you are hovering at low altitude in a hot-air balloon, accelerated neither upward or downward. The total wieght of the balloon, including its load and the hot air in it is 20,000N. Show that the volume of the displaced air is 1700 m3 (Hint:Buoyancy in a Gas)

Answer 1

You need to know the density of outside air to do this. Assume 1 atmosphere and 20 C and see what you get. The density under those conditions is about 1.19 kg/m^3, but it also depends somewhat upon the humidity

The weight of the displaced air is
(1.19) g V = 20,000 N
g is the acceleration of gravity, 9.8 m/s^2.

V = ?

The answer will not be exactly 1700 m^3, but is pretty close. Since they did not specify the air temperature, an exact answer cannot be expected.