Wind blows at an average speed of 5m/s 10% of the time. If the efficienty is 45%, what is the radius of the wind turbine that would be needed to generate 571 W of electricity. density of air = 1.25 kg/m^3 The formula is Power = η(1/2*pi*r^2*ρ*v^3), where η is the efficiency, ρ the density, and v the average velocity, r = radius. Would the average speed be just 0.5 m/s ? Thanks.