First slide

Fluid dynamics

Question

Air streams horizontally across an aeroplane wing of area 3m² weighing 250 kg. The air speed is 60 m/s and 45 m/s over the top surface and under the bottom surface respectively. What is the lift on the wing ? (Density of air 1.293 g/l)

Easy

A

3000 N
B

3500N
C

4000N
D

3054N

Solution

A = 3m², m = 250kg
$ρ = 1.293 g m / l = 1.293 \times \frac{10^{- 3}}{10^{- 3}} k g / m^{3}$

V₁ = 60m/s, V₂ = 45m/s

$\large F=(P_2-P_1)A=\frac 12\rho\left ( V_1^2- V_2^2 \right )\times A$

$\large =\frac {1.293}{2}\left [ 60^2-45^2 \right ](3)=3054N$

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