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Old 03-27-10, 07:01 PM   #1
AchiLLe..s
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Physics 2 Web assign help

Ight, Ive got these 2 problems I cannot figure out for the life of me. Maybe you guys can be of some assistance.

#1) You are preparing some apparatus for a visit to a newly discovered planet Caasi having oceans of glycerine and a surface acceleration due to gravity of 3.20 m/s2. If your apparatus floats in the oceans on earth with 23.0% of its volume submerged, what percentage will be submerged in the glycerine oceans of Caasi?

#2) Lift on an Airplane. Air streams horizontally past a small airplane's wings such that the speed is 70.0 m/s over the top surface and 46.0 m/s past the bottom surface. If the plane has a wing area of 16.6 m2 on the top and on the bottom, what is the net vertical force that the air exerts on the airplane? The density of the air is 1.20 kg/m3.


I think for #2 Im supposed to use burnoullis equation, but there is no Y height in the question.

Thanks. This is due at 11:00 tonight by the way
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Old 03-27-10, 07:21 PM   #2
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1 is a simple Delta change problem. Figure the percentage of gravitic attraction on Caasi of that of Earth as a decimal, and the object will ride that much higher + the amount higher based on the difference of density between Glycerine and H2O.

Water density is Water 62.4lbs/foot^3 and Glycerine is 78.6 lbs/foot^3

F_net = m_b g-B | B = rho V_f g
R = V_f/V_b | |
R | fraction of body submerged
V_b | volume of body
rho | fluid density
F_net | effective gravity
m_b | mass of body
B | buoyancy force in fluid
V_f | volume of replaced fluid
g | acceleration due to gravity (~~ 9.807 m/s^2) (One Earth Gravity)

3.2/9.807ms^2=0.32629754257163250739267869888855, or .
32.629754257163250739267869888855% of the surface gravity of Earth.

There are all your variables. Work it through. It will be 2 problems, the delta change based on the gravity difference, and then Archimedes principal, focusing on displacement and submerged volume.
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Old 03-27-10, 08:19 PM   #3
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Based on Tom's reply, I believe he weighs the same as a duck.
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Old 03-27-10, 08:42 PM   #4
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American duck or European?
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Old 03-28-10, 08:59 PM   #5
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#1) The magnitude of the gravitational field is irrelevant. All that matters are the densities of the item and the fluids involved. An item floats if its weight is less than the weight of an equal volume of the fluid. Since both the item and the fluid are subject to the same gravitational field, you can use mass instead of weight in your calculations, and ignore the value of g. Look up the density of ocean water and the density of glycerine.

Last edited by deraltekluge; 03-28-10 at 09:08 PM.
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