fryer (vdf96) – Fluid Mechanics – graves – (6)
1
This
printout
should
have
30
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
10.0points
In a deep dive, a whale is appreciably com
pressed by the pressure of the surrounding
water.
What happens to the whale’s density?
1.
Its density increases.
correct
2.
It cannot be determined.
3.
Its density remains the same as before.
4.
Its density decreases.
Explanation:
Since the mass is unchanged and the volume
decreases, the density of the whale increases.
002
10.0points
An engineer weighs a sample of mercury (
ρ
=
13
.
6
×
10
3
kg
/
m
3
) and finds that the weight
of the sample is 7
.
0 N.
What is the sample’s volume? The acceler
ation of gravity is 9
.
81 m
/
s
2
.
Correct answer: 5
.
24675
×
10

5
m
3
.
Explanation:
Let :
W
= 7
.
0 N
,
ρ
= 13
.
6
×
10
3
kg
/
m
3
,
and
g
= 9
.
81 m
/
s
2
.
m
=
W
g
so
V
=
m
ρ
=
W
g ρ
=
7 N
(9
.
81 m
/
s
2
)(13
.
6
×
10
3
kg
/
m
3
)
=
5
.
24675
×
10

5
m
3
.
003
10.0points
Air within the funnel of a large tornado may
have a pressure of only 0
.
56 atm.
What is the approximate outward force
F
on a 7
.
6 m
×
22 m wall if a tornado suddenly
envelopes the house? Atmospheric pressure is
1
.
013
×
10
5
Pa.
Correct answer: 7
.
45244
×
10
6
N.
Explanation:
Let :
P
0
= 1 atm = 1
.
013
×
10
5
Pa
,
P
= 0
.
56 atm
,
a
= 7
.
6 m
,
and
b
= 22 m
.
The inside pressure is 1 atm since the tor
nado envelopes the house suddenly. The force
due to the air inside the house (pointing out
ward) is
F
outward
=
P
0
A
=
P
0
a b
= (1
.
013
×
10
5
Pa) (7
.
6 m) (22 m)
= 1
.
69374
×
10
7
N
.
The inward force due to the air outside the
house is
F
inward
=
P A
=
P a b
= (0
.
56 atm) (7
.
6 m) (22 m)
×
1
.
013
×
10
5
Pa
atm
= 9
.
48492
×
10
6
N
,
so the net force on the house is
F
=
F
outward
−
F
inward
= 1
.
69374
×
10
7
N
−
9
.
48492
×
10
6
N
=
7
.
45244
×
10
6
N
.
004(part1of2)10.0points
In a car lift used in a service station, com
pressed air exerts a force on a small piston
of circular crosssection having a radius of
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fryer (vdf96) – Fluid Mechanics – graves – (6)
2
4
.
26 cm.
This pressure is transmitted by a
liquid to a second piston of radius 16
.
6 cm.
What force must the compressed air exert
in order to lift a car weighing 13200 N?
Correct answer: 869
.
315 N.
Explanation:
Let :
r
1
= 4
.
26 cm
,
r
2
= 16
.
6 cm
,
and
F
2
= 13200 N
.
Because
the
pressure
exerted
by
the
compressed air is transmitted undiminished
throughout the fluid,
F
1
A
1
=
F
2
A
2
F
1
=
parenleftbigg
A
1
A
2
parenrightbigg
F
2
=
parenleftbigg
π r
2
1
π r
2
2
parenrightbigg
F
2
=
(4
.
26 cm)
2
(16
.
6 cm)
2
(13200 N)
=
869
.
315 N
.
005(part2of2)10.0points
What air pressure will produce this force?
Correct answer: 1
.
52478
×
10
5
Pa.
Explanation:
P
=
F
1
A
1
=
F
1
π r
2
1
=
869
.
315 N
π
(4
.
26 cm)
2
parenleftbigg
100 cm
1 m
parenrightbigg
2
=
1
.
52478
×
10
5
Pa
.
006
10.0points
Why is the gas pressure inside an inflated
balloon always greater than the air pressure
outside?
1.
Warmer air is inside the balloon.
2.
Cooler air is inside the balloon.
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 Fall '10
 Graves
 Physics, mechanics, Orders of magnitude, Pressure measurement

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