The speed of flow past the lower surface of a wing of an aeroplane is `50ms^(-1)`. What speed of flow over the upper surface will give a dynamic lift of `1000 Pa`? Density of air `=1.3 kgm^(-3)`

Options

A. `25.55 m//s`
B. `63.55m//s`
C. `13.25m//s`
D. None of these

Answer

B

Explanation

Applying Bernoulli's theorem to the lower and upper surface of a wing

`P_(1) = 1/2 rho v_(1)^(2) = P_(2) + 1/2 rho v_(2)^(2)`
or `P_(1)-P_(2) = 1/2 rho (v_(2)^(2)-v_(1)^(2))`
`implies 1000 = 1/2xx1.30(v_(2)^(2)-50^(2))` [ `:. lift = P_(1)-P_(2)]`
or `v_(2)^(2)-2500 = 200//1.3`
or, `v_(2) = 63.55 m//s`.