Question

In a test experiment on a model aeroplane in a wind tunnel, the flow speeds on the upper and lower surfaces of the wing are $70m{s}^{-1}$ and $63m{s}^{-1}$ respectively. What is the lift on the wing, if its area is $2.5m^2$ ? Take the density of air to be $1.3kg{m}^{-3}$.

• A. $1513N$
• B. $1513dynes$
• C. $151.3N$
• D. $151.3dynes$

Answer 1

The correct option is A $1513N$

Applying Bernoulli's principle to above and below the using,
$P_1+\frac{1}{2}P{V}_1^2=P_2+\frac{1}{2}P{V}_2^2$
$\Rightarrow P_1-P_2=\frac{1}{2}\times 1.3\times ({70}^2-{63}^2)$
$\Rightarrow$ Pressure differnece across sing = $605.15N/m^2$
Lift on the using = pressure difference across surface of using $\times$ Area.
$=605.15N/m^2\times 2.5m^2$
$=1512.875N$
$\approx 1513N$