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

Water is flowing through two horizontal pipes of different diameters which are connected together. The diameters of the two pipes are $3\, cm$ and $6\, cm$ respectively. If the speed of water in the narrower pipe is $4\, m/s$ and the pressure is $2.0 \times 10^4\, Pa$,then the speed of water in the wider pipe is ........ $m/s$.

Two water pipes of diameter $2 \,cm$ and $4 \,cm$ are separately connected to a main supply line. The velocity of flow of water in the pipe of $2 \,cm$ diameter is

The radius of the cross-section of the cylindrical tube of a spray pump is $2 \,cm$. One end of the pump has $50$ fine holes, each of radius $0.4 \,mm$. If the speed of flow of the liquid inside the tube is $0.04 \,ms^{-1}$, what is the speed of ejection of the liquid from the holes (in $\,ms^{-1}$)?

Explain steady flow.

The cylindrical tube of a spray pump has a cross-section of $8 \,cm^{2}$, one end of which has $40$ fine holes each of area $10^{-8} \,m^{2}$. If the liquid flows inside the tube with a speed of $0.15 \,m \,min^{-1}$, the speed with which the liquid is ejected through the holes is (in $\,ms^{-1}$)