Water (of density $\varrho$) flows steadily through a horizontal pipe of variable cross-section. If the pressure of water is $P$ at a point where the flow speed is $V$,then the pressure at another point where the flow speed becomes $3V$ is:

The correct Bernoulli's equation is (symbols have their usual meaning):

Water from a tap emerges vertically downwards with an initial velocity of $4 \,m/s$. The cross-sectional area of the tap is $A$. The flow is steady and the pressure is constant throughout the stream of water. The distance $h$ vertically below the tap,where the cross-sectional area of the stream becomes $\frac{2}{3} A$,is (take $g = 10 \,m/s^2$): (in $\,m$)

Explain why the roof of a building flies off during a stormy wind.

In a test experiment on a model aeroplane in a wind tunnel,the flow speeds on the upper and lower surfaces of the wing are $70 \; m s^{-1}$ and $63 \; m s^{-1}$ respectively. What is the lift on the wing if its area is $2.5 \; m^{2}$? Take the density of air to be $1.3 \; kg m^{-3}$.

Air streams horizontally past an airplane. The speed over the top surface is $60 \, m/s$ and that under the bottom surface is $45 \, m/s$. The density of air is $1.293 \, kg/m^3$. The difference in pressure is ....... $N/m^2$.