Question 691
CBSE Class 11 Physics · Mechanical Properties of Fluids · Fluid flow and Bernoulli principle
Air speeds above and below a model wing are 70 and \(63\,\mathrm{m\,s}\)⁻¹. For wing area 2.5 m² and air density \(1.3\,\mathrm{kg\,m}\)⁻³, find the lift.
Solution to Question 691
Complete workingPrinciple and reasoning. Work from the governing physical relation and apply it to every stated part.
Apply Bernoulli's equation at equal heights. Faster air above has lower pressure.
\[\Delta P=\frac12\rho(v_{\rm upper}^2-v_{\rm lower}^2)\]
\[=\frac12(1.3)(70^2-63^2)=605\ \mathrm{Pa}\]
\[\begin{aligned}F_L &= \Delta PA\\&= (605)(2.5)\\&= 1.51\times10^3\ \mathrm N\end{aligned}\]
Final answer
\[1.51\times10^3\ \mathrm N\text{ upward}\]