The speed of air moving over the top of a thin airfoil, such as an airplane wing, is 50 m/s. The speed of air moving under the airfoil is 40 m/s. If the area of the surface is 30 m^2, what is the lift force on the airfoil due to the moving air.
Assume air has a density of 1.29 kg/m^3.
oldprof
Can't tell as we are not given the coefficient of lift Cl.
But in general the lift force L = 1/2 rho Cl A V^2; where rho = 1.29 kg/m^3, A = 30 m^2, and V = 50 mps.
When you don't know the value of a factor like Cl, do what we do in the real world and put in a range of values to see how critical that factor is to the final answer. For a jet, Cl is typically small as the velocity V is high. Of course, if you know the weight of the plane, you can actually solve for Cl = 2W/(rho A V^2) where W is the weight.