Momentum and CollisionHard
Question
Air is streaming past a horizontal aeroplane wing such that its speed is 120 m/s over the upper surface and 90 m/s at the lower surface. If the density of air is 1.3 kg/m3 and the wing is 10 m long and has an average width of 2 m, then the difference of the pressure on the two sides of the wing is :-
Options
A.40.95 N/m2
B.409.5 N/m2
C.4095 N/m2
D.40950 N/m2
Solution
Using Bernoulli′s theorem
P1 +
ρv12 + ρgh1 = P2 + 
ρv22 + ρgh2
For the horizontal motion of the plane h1 = h2, then
P1 +
ρv12 = P2 + 
ρv22
or P2 - P1 =
ρ(V12 - V22)
=
× 1.3[1202 - 902]
= 0.65[210 × 30] = 4095 N/m2
P1 +
ρv12 + ρgh1 = P2 + ρv22 + ρgh2For the horizontal motion of the plane h1 = h2, then
P1 +
ρv12 = P2 + ρv22or P2 - P1 =
ρ(V12 - V22)=
× 1.3[1202 - 902]= 0.65[210 × 30] = 4095 N/m2
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