A windmill is operating in a 10 m/s wind that has a density of 1.2 kg/m^3. The diameter of the windmill is 4 m. The constant-pressure (atmospheric) stream tube has a diameter of 3 m upstream of the windmill and 4.5 m downstream. Assume that the velocity distributions are uniform and the air is incompressible. Determine the thrust force on the windmill.