. A hall has a volume of 240 m3. An air-conditioning system is to replace the air in this hall every thirty minutes, using ducts that have a square cross section. Assuming that air can be treated as an incompressible fluid, find the length of a side of the square if the air speed within the ducts is 6.0 m/s.
(area * length)/time = volume/time
area * 6.0m/s = 240m^3/1800s
area = 240/1800 * 1/6 = 40/1800 = 1/45 m^2
so the side is 14.9 cm