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 $\,m$)

Why is it dangerous to stand on the edge of a platform near the tracks when a train is passing at high speed? Explain.

The weight of an aeroplane flying in the air is balanced by:

$A$ Venturimeter is used to:

Give the formula for the measurement of the velocity of a fluid in the broader part of a venturi-meter.

The Pitot tube shown in the figure is used to measure fluid flow velocity in a pipe of cross-sectional area $S$. It was invented by a French engineer Henri Pitot in the early $18^{th}$ century. The volume of the gas flowing across the section of the pipe per unit time is (The difference in the liquid columns is $\Delta h$,$\rho_0$ and $\rho$ are the densities of liquid and the gas respectively):