question_answer 21)

The blades of a windmill sweep out a circle of area A. (a) If the wind flows at a velocity v perpendicular to the circle, what is the mass of the air passing through it in time t ? (b) What is the kinetic energy of the air ? (c) Assume that the windmill converts 25% of the wind's energy into electrical energy, and that  and the density of air is . What is the electrical power produced ?  

Answer:

(a) Volume of the air passing through the windmill in time t = Area of circle x distance covered by wind in time t   Mass of the air passing through the windmill in time t, m = Density x volume. (b) Kinetic energy of the air is  . (c) K.E. of air converted into electrical energy in time t  of   Electrical power produced