An incompressible fluid flows steadily through a horizontal cylindrical pipe. The pipe has radius $3R$ at point $A$ and $1.5R$ at point $B$, further along the flow direction at the same level. If the velocity at point $A$ is $v$, then the velocity at point $B$ 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 $\,ms^{-1}$)?

$A$ laminar stream is flowing vertically down from a tap of cross-section area $1 \ cm^2$. At a distance $10 \ cm$ below the tap,the cross-section area of the stream has reduced to $0.5 \ cm^2$. The volumetric flow rate of water from the tap is about ........ $litre/min$.

$A$ river gradually deepens from a depth of $4 \ m$ to a depth of $8 \ m$ as shown. The width,$W$,of the river does not change. At the depth of $4 \ m$,the river's speed is $12 \ m/s$. Its velocity at the $8 \ m$ depth is ......... $m/s$.

Explain the concept of a tube of flow.

$A$ motor of power $P_0$ is used to deliver water at a certain rate through a given horizontal pipe. To increase the rate of flow of water through the same pipe $n$ times, the power of the motor is increased to $P_1$. The ratio of $P_1$ to $P_0$ is