# Q21 (a) The blades of a windmill sweep out a circle of area 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?

Answers (1)
D Devendra Khairwa

The volume of wind   =   $Av$$\rhov$ here  $A$ is the swept circle and $v$ is the velocity.

Thus the mass of the wind is  : -    $\rho Av$  ,  $\rho$   is the density of the air.

Hence mass of wind flowing through windmill in time t is     $=\ \rho Avt$.

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