$A$ plane is in level flight at constant speed and each of its two wings has an area of $40 \,m^2$. If the speed of the air is $180 \,km/h$ over the lower wing surface and $252 \,km/h$ over the upper wing surface,the mass of the plane is . . . . . . $kg$. (Take air density to be $1 \,kg \,m^{-3}$ and $g=10 \,ms^{-2}$)

Explain with the help of Bernoulli's principle why a spinning ball follows a curved path during flight.

The venturi-meter works on:

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 $\,m$)

Water flows through a frictionless duct with a cross-section varying as shown in the figure. The pressure $p$ at points along the axis is represented by:

In the following figure,the flow of liquid through a horizontal pipe is shown. Three tubes $A, B$ and $C$ are connected to the pipe. The radii of the tubes $A, B$ and $C$ at the junction are respectively $2 \ cm, 1 \ cm$ and $2 \ cm$. It can be said that the: