In a test experiment on a model aeroplane in wind tunnel, the flow speeds on the upper and lower surfaces of the wings are $70 \mathrm{~ms}^{-1}$ and $65 \mathrm{~ms}^{-1}$ respectively. If the wing area is $2 \mathrm{~m}^{2}$ the lift of the wing is $\_\_\_\_$ N. (Given density of air $=1.2 \mathrm{~kg~m}^{-3}$)

JEE Main · 2024 · 29 Jan 2024 · Shift 1 · Fluid Mechanics

In a test experiment on a model aeroplane in wind tunnel, the flow speeds on the upper and lower surfaces of the wings are

70 ms^{- 1}

and

65 ms^{- 1}

respectively. If the wing area is

2 m^{2}

the lift of the wing is

____

N.
(Given density of air

= 1.2 kg m^{- 3}

)

Answer: 810

Solution

By Bernoulli's principle, the pressure difference between the lower and upper surfaces gives a lift:

F = \frac{1}{2} ρ (v_{1}^{2} - v_{2}^{2}) A = \frac{1}{2} (1.2) (7 0^{2} - 6 5^{2}) (2)

= 0.6 \times 675 \times 2 = 810 N

Key confirmed: 810.

JEE Main · 2024 · 29 Jan 2024 · Shift 1 · Integer answer

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