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ME111 – FLUID MECHANICS
Key to Examination
#1
Spring 2008
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1.
Someone claims that the absolute pressure in a liquid of constant density doubles when the depth is doubled.
Do you
agree?
Explain your answer.
A simple Yes or No answer will receive zero credit.
No.
By definition, at a depth of z, the absolute pressure is expressed as
P
abs
=
P
atm
+
γ
z, and the gage pressure as
z.
It should be obvious that doubling the depth will not result in doubling of the absolute pressure, but it would result
in doubling of the gage pressure.
2.
Consider two 5cmdiameter spherical balls – one made of aluminum (
ρ
= 2700 kg/m
3
), the other of iron (
ρ
= 8000
kg/m
3
) – submerged in water.
Will the buoyant forces acting on these two balls be the same or different?
Explain
your answer.
A simple Yes or No answer will receive zero credit.
Yes, they will be the same.
Buoyant force on a body submerged in a fluid is equal to the weight of the displaced volume
of the fluid.
That is, F
b
=
∀
, where
is the specific weight of the fluid and
is the displaced volume.
The displaced
volume is equal to the volume of the solid body.
Given that the two spheres have the same diameter (i.e., same
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 Spring '08
 USaxena
 Fluid Dynamics, 5 cm, 5 ft, 5 mm, 0 W

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