A windmill, such as that in the opening photograph of this chapter, turns in response to a force of high-speed air resistance, R = ½ D/Av2. The power available is P = Rv = ½Dpur2v3, where v is the wind speed and we have assumed a circular face for the windmill, of radius r. Take the drag coefficient as D = 1.00 and the density of air from the front endpaper. For a home windmill with r = 1.50 m, calculate the power available if (a) v = 8.00 m/s and (b) v = 24.0 m/s. The power delivered to the generator is limited by the efficiency of the system, which is about 25%. For comparison, a typical home needs about 3 kW of electric power.