Q. Air is streaming past a horizontal air plane wing such that its speed is $120\ ms^{- 1}$ over the upper surface and $90\ \ ms^{- 1}$ at the lower surface. If the density of air is $1.3\ kgm^{- 3}$, what will be the gross life on the wing? If the wing is $10\ m$ long and has an average width of 2 m,
A) 81.9 N
B) 8.19 kN
C) 81.9 kN
D) 819 kN
Explanation
(c) $p_{1} + \frac{1}{2}\rho\ v_{1}^{2} = p_{2} + \frac{1}{2}\rho\ v_{2}^{2}$
Or $p_{1} - p_{2} = \frac{1}{2}\rho\ (v_{2}^{2} - v_{1}^{2})$
$= \frac{1}{2} \times 1.3 \times (120^{2} - 90^{2})$
$= 4.095 \times 10^{3}\ Nm^{- 2}$
Gross lift on the wing $= (p_{1} - p_{2}) \times$ area
$= 4.095 \times 10^{3} \times 10 \times 2$
$= 81.9 \times 10^{3}$ N
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.