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 $\underline{\hspace{2cm}}N$. (Given density of air $=1.2 \mathrm{~kg} \mathrm{~m}^{-3}$)