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~christina~
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Homework Statement
An airplane has a mass of 1.60x10^4 kg and each wing has an area of 40.0m^2. During level flight the pressure on the lower wing surface is 7.00x10^4 Pa. Determine the pressure on the upper wing surface.
http://img168.imageshack.us/img168/617/41426717vo3.th.jpg [Broken]
Homework Equations
[tex]\sum F= F_L -F_u - F_{mg} = 0 [/tex]
The Attempt at a Solution
My basic problem is that I keep getting a negative number for the pressure which is odd
[tex]\sum F= F_L -F_u - F_{mg} = 0 [/tex]
[tex] F_u = F_{mg}- F_L [/tex]
P= F/A
[tex] P_u= Mg - P_L A [/tex]
[tex]((9.8m/s^2)*(1.60x10^4kg))-((40.0m^2)(7.00x10^4Pa))= P_u[/tex]
[tex]-2,643,200 = P_u A [/tex]
[tex] P_u= -66,080 Pa [/tex] =>
my problem is why is it negative?? is it because it's force is downward??
Plus..the answer that was given (only the answer) was 6.80x10^4 Pa so I must have done something wrong. However I ccalculated it 3 times and I still get the same answer.
Thank you very much =D
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