Find mechanical power?

Question

The blades of a wind mill sweep out a circle of area A.If wind flows with velocity v perpendicular to blades of wind mill and its density is D,then the mechanical power received by wind mill is
(a) (DAv^3)/2
(b) DAv^3
(c) (DAv^2)/2
(d) 2DAv^2

Answer 1

P = 1/2 D A v³

The correct answer is (a)