An aircraft of mass $3 \times 10^5 \ kg$ with total wing area $400 \ m^2$ is in a level flight at a speed of $540 \ km \ h^{-1}$. The density of air at its height is $1.2 \ kg \ m^{-3}$. The fractional increase in the speed of the air on the upper surface of its wings relative to the lower surface is . . . . . . $\left(g=10 \ ms^{-2}\right)$

The speeds of air above and below the wing of an airplane are $120\, m/s$ and $90\, m/s$,respectively. The density of air is $1.3\, kg/m^3$. If the wing has a length of $10\, m$ and a width of $2\, m$,the pressure difference between the top and bottom of the wing is ......... $Pascal$.

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

The pressure of water in a water pipe when the tap is closed and opened is $3.5 \times 10^5 \, N/m^2$ and $3 \times 10^5 \, N/m^2$ respectively. With the tap open,the velocity of water flowing is ........... $m/s$. (Take density of water $\rho = 10^3 \, kg/m^3$)

An ideal gas of density $\rho_1=0.2 \ kg \ m^{-3}$ enters a chimney of height $h$ at the rate of $\alpha=0.8 \ kg \ s^{-1}$ from its lower end,and escapes through the upper end as shown in the figure. The cross-sectional area of the lower end is $A_1=0.1 \ m^2$ and the upper end is $A_2=0.4 \ m^2$. The pressure and the temperature of the gas at the lower end are $600 \ Pa$ and $300 \ K$,respectively,while its temperature at the upper end is $150 \ K$. The chimney is heat insulated so that the gas undergoes adiabatic expansion. Take $g=10 \ ms^{-2}$ and the ratio of specific heats of the gas $\gamma=2$. Ignore atmospheric pressure. Which of the following statement$(s)$ is(are) correct?

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