A student builds a simple axial flow-ventilating fan driven by a motor to provide some relief during summer. The motor delivers 0.4 kW of power to the fan blades. She observes the fan produces an outlet stream of air with a diameter of 0.6 m having a speed of 12 m/s. Assume that the flow upstream of the fan has negligible speed. Assume density of air to be 1.23 kg/m3 and room temperature to be 20o C. Assume all losses are due to friction (heat).
[a] Determine how much power from the motor produces useful effects (for the student).
[b] Estimate the mechanical efficiency of this fan.