Suppose a horizontal-axis wind turbine, which has a mechanical efficiency of = 0.8, is used to drive a water pump directly via the rotation of its shaft, and that the power output of the turbine after mechanical losses is 8 kW. If the atmospheric conditions in the vicinity of the wind turbine have temperature 22.9 C and pressure 101.6 kPa, and the wind turbine has radius 8.4 m, what is the minimum windspeed in m s^-1 needed to run the pump