The blades of a windmill sweep out a circle of area $A$. If the wind flows at a velocity $b$ perpendicular to the circle, then the mass of the air of density $\rho $ passing through it in time $t$ is
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Volume of wind flowing per second $= Av$
Mass of wind flowing per second $= Av\rho $
Mass of air passing in time $t$ is $= Av\rho t$
Mass of wind flowing per second $= Av\rho $
Mass of air passing in time $t$ is $= Av\rho t$
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