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Water flows steadly through a horizontal pipe of non-uniform cross section. If the pressure of water is $4 * 10^6\;N/m^2$ at a point where the velocity of flow is $2\;m/s$ and cross section is $0.02\;m^2$, what is the pressure at a point where cross-section reduces to $0.01\;m^2$?

Calculate mass of an aeroplane with the wings of area $55\;m^2$ flying horizontally. The velocity of air above and below the wings is $155\;m/s$ and $140\;m/s$ respectively.