Question

A light aircraft has a wing area of $15m^2$ and flies at $60m/s$ in level flight. If the air velocity over the upper surface of the wing is $15\%$ greater, then the magnitude of the lift developed (in $N$) is (nearly)

(given: density of air is $1.2kg/m^3$)

• A. $5255$
• B. $7500$
• C. $2525$
• D. $10450$

Answer 1

The correct option is D $10450$

Velocity of air in upper wing$=\frac{115}{100}\times 60=69m/s$
So,
Pressure difference across the wings
$\frac{1}{2}\times 1.2\times ({69}^2-{60}^2)Pa$
$=696.6Pa$
So,
Magnitude of life developed $=$ pressure diff $\times$ Area
$=(696.6\times 15)N\approx 10449N$