The speeds of air-flow on the upper and lower surfaces of a wing of an airplane are v₁ and v₂ respectively. If A is the cross-sectional area of the wing and 'p' is the density of air, then the upward lift is

Air moves over an airplane's wings faster when it is in flight due to its unique form than over its lower surface. According to the Bernoullis principle, this difference in air speeds above and below the wings provides a difference in pressure, which causes a force termed dynamic lift to act upward on the plate.

${\mathrm{P}}_{\mathrm{u}}+ \frac{1}{2}\mathrm{p}{{\mathrm{v}}_1}^2={\mathrm{P}}_1+\frac{1}{2}\mathrm{p}{{\mathrm{v}}_2}^2$

${\mathrm{P}}_1-{\mathrm{P}}_{\mathrm{u}}=\frac{1}{2}\mathrm{p}({{\mathrm{v}}_1}^2-{{\mathrm{v}}_2}^2)$

$\mathrm{Upward} \mathrm{lift} = \mathrm{pressure} \mathrm{difference} \times \mathrm{area} \mathrm{of} \mathrm{wing}$

$\mathrm{Upward} \mathrm{lift} =\frac{1}{2}\mathrm{pA}({{\mathrm{v}}_1}^2-{{\mathrm{v}}_2}^2)$

Hence the correct answer is $\frac{1}{2}\mathrm{pA}({{\mathrm{v}}_1}^2-{{\mathrm{v}}_2}^2).$