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Old Jan 5th 2010, 05:28 AM   #1
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Join Date: Nov 2009
Location: California
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Unhappy Application of Bernoulli's Equation (kinda simple)

ok so I got this in class and was trying to figure it out but part b didn't make sense to me and i will show why not when I get there.

65. (A) Find the pressure difference on an airplane wing if air flows over the upper surface with a speed of 115 m/s and along the bottom surface with a speed of 105 m/s. (B) If the area of the wing is 32 m^2, what is the net upward force exerted on the wing?

OK so I used Bernoulli's equation (duh) to calculate the first part going from
P1 + .5pv1^2 = P2 + .5pv2^2 w V1=115 & v2=105

then i plugged everything in trying to find change in Pressure using
1.29 kg/m^3 as density and got change in P=1419

alright, now on b i know the formula P=F/A and I know I have A but I do not understand where to get this new P for the F exerted up. My lab partners told be to just use the difference in P but that totally does not make sense and I am wondering why that would work. PLEASE HELP!!!
and thank you ahead of time!

Last edited by I<3Kinematics; Jan 5th 2010 at 05:29 AM. Reason: spelling error
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Old Jan 5th 2010, 07:41 AM   #2
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if i split the problem into 2 parts, perhaps it may make sense.
say i have P1 air pressure above the wing and P2 air pressure below the wings. so force exerted by P1 on wing= P1 A downward.
force exerted by P2 on wing= P2 A upwards.
so net force upward=P2 A- P1 A=(P2-P1)A =pressure difference*area
hope that helps.
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