Question

The blades of a windmill sweep out a circle of area $A$. If the wind flows at a velocity $v$ perpendicular to the circle, then the mass of the air of density $\rho$ passing through it in time $t$ is:

• A. $Av\rho t$
• B. $2Av\rho t$
• C. $A{v}^2\rho t$
• D. $\frac{1}{2}Av\rho t$

Answer 1

The correct option is A $Av\rho t$

Volume of wind flowing per second $=Av$
Mass of wind flowing per second $=Av\rho$
Mass of air passing in time $ts=Av\rho t$.