Air is streaming past a horizontal aeroplane wing such that its speed is $120\, m/s$ over the upper surface and $90\, m/s$ at the lower surface. If the density of air is $1.3\, kg/m^3$ and the wing is $10\, m$ long and has an average width of $2\, m$,then the difference of the pressure on the two sides of the wing is ........ $N/m^2$.

Why does an airplane run a certain length on the runway first before taking off?

Figures $(a)$ and $(b)$ refer to the steady flow of a non-viscous liquid. Which of the two figures is incorrect? Why?

An $L$-shaped tube with a small orifice is held in a water stream as shown in the figure. The upper end of the tube is $10.6 \ cm$ above the surface of the water. What will be the height (in $cm$) of the jet of water coming from the orifice? The velocity of the water stream is $2.45 \ m/s$. (Take $g = 9.8 \ m/s^2$)

The area of cross-section of a large tank is $0.5 \; m^{2}$. It has a narrow opening near the bottom having an area of cross-section $1 \; cm^{2}$. $A$ load of $25 \; kg$ is applied on the water at the top in the tank. Neglecting the speed of water in the tank,the velocity of the water coming out of the opening at the time when the height of water level in the tank is $40 \; cm$ above the bottom will be $\dots \; cm \; s^{-1}$. [Take $g = 10 \; m \; s^{-2}$]

The pans of a physical balance are in equilibrium. Air is blown under the right hand pan; then the right hand pan will