Problems
445
(a) What is the minimum pressure at which the water must
be pumped if it is to arrive at the village? (b) If 4 500 m
3
are pumped per day, what is the speed of the water in the
pipe? (c) What additional pressure is necessary to deliver
this flow? Note : Assume that the free-fall acceleration and
the density of air are constant over this range of elevations.
46.
Old Faithful Geyser in Yellowstone Park (Fig. P14.46) erupts
at approximately 1-h intervals, and the height of the water
column reaches 40.0 m. (a) Model the rising stream as a se-
ries of separate drops. Analyze the free-fall motion of one of
the drops to determine the speed at which the water leaves
the ground. (b) What If? Model the rising stream as an ideal
fluid in streamline flow. Use Bernoulli’s equation to deter-
mine the speed of the water as it leaves ground level.
(c) What is the pressure (above atmospheric) in the heated
underground chamber if its depth is 175 m? You may assume
that the chamber is large compared with the geyser’s vent.
50. An airplane is cruising at an altitude of 10 km. The pressure
outside the craft is 0.287 atm; within the passenger compart-
ment the pressure is 1.00 atm and the temperature is 20°C.
A small leak occurs in one of the window seals in the passen-
ger compartment. Model the air as an ideal fluid to find the
speed of the stream of air flowing through the leak.
51.
A siphon is used to drain water from a tank, as illustrated in
Figure P14.51. The siphon has a uniform diameter. Assume
steady flow without friction. (a) If the distance h ! 1.00 m,
find the speed of outflow at the end of the siphon.
(b) What If? What is the limitation on the height of the top
of the siphon above the water surface? (For the flow of the
liquid to be continuous, the pressure must not drop below
the vapor pressure of the liquid.)
Figure P14.46
Mercury
v
air
A
∆h
Figure P14.49
v
h
y
ρ
Figure P14.51
47. A Venturi tube may be used as a fluid flow meter (see Fig.
14.20). If the difference in pressure is P
1
&
P
2
!
21.0 kPa,
find the fluid flow rate in cubic meters per second,
given that the radius of the outlet tube is 1.00 cm, the
radius of the inlet tube is 2.00 cm, and the fluid is gasoline
($ ! 700 kg/m
3
).
Section 14.7 Other Applications of Fluid Dynamics
48. An airplane has a mass of 1.60 " 10
4
kg, and each wing
has an area of 40.0 m
2
. During level flight, the pressure on
the lower wing surface is 7.00 " 10
4
Pa. Determine the
pressure on the upper wing surface.
49.
A Pitot tube can be used to determine the velocity of air
flow by measuring the difference between the total pres-
sure and the static pressure (Fig. P14.49). If the fluid
in the tube is mercury, density $
Hg
!
13 600 kg/m
3
, and
'
h ! 5.00 cm, find the speed of air flow. (Assume that the
air is stagnant at point A, and take $
air
!
1.25 kg/m
3
.)
52.
The Bernoulli effect can have important consequences for
the design of buildings. For example, wind can blow
around a skyscraper at remarkably high speed, creating
low pressure. The higher atmospheric pressure in the still
air inside the buildings can cause windows to pop out. As
originally constructed, the John Hancock building in
Boston popped window panes, which fell many stories to
the sidewalk below. (a) Suppose that a horizontal wind
blows in streamline flow with a speed of 11.2 m/s outside a
large pane of plate glass with dimensions 4.00 m " 1.50 m.
Assume the density of the air to be uniform at 1.30 kg/m
3
.
The air inside the building is at atmospheric pressure.
What is the total force exerted by air on the window pane?
(b) What If? If a second skyscraper is built nearby, the air
speed can be especially high where wind passes through
the narrow separation between the buildings. Solve part
(a) again if the wind speed is 22.4 m/s, twice as high.
53.
A hypodermic syringe contains a medicine with the density
of water (Figure P14.53). The barrel of the syringe has a
cross-sectional area A ! 2.50 " 10
&
5
m
2
, and the needle has
a cross-sectional area a ! 1.00 " 10
&
8
m
2
. In the absence of
a force on the plunger, the pressure everywhere is 1 atm. A
force F of magnitude 2.00 N acts on the plunger, making
medicine squirt horizontally from the needle. Determine the
speed of the medicine as it leaves the needle’s tip.
Stan Osolinski/Dembinsky Photo Associates
A
a
F
v
Figure P14.53