alexander (jra2623) – homework 25 – Turner – (92510)
1
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001
10.0 points
Water is to be pumped to the top of the
Empire State Building, which is 1200 ft high.
What gauge pressure is needed in the wa
ter line at the base of the building to raise the
water to a height of 708 ft? Assume the den
sity of water is 1000 kg
/
m
3
. The acceleration
of gravity is 9
.
8 m
/
s
2
.
Correct answer: 2
.
11472
×
10
6
Pa.
Explanation:
Let :
h
= 708 ft
and
ρ
= 1000 kg
/
m
3
.
P
g
=
P

P
atm
=
ρ g h
=
(
1000 kg
/
m
3
)(
9
.
8 m
/
s
2
)
×
(708 ft)
parenleftbigg
1 m
3
.
281 ft
parenrightbigg
=
2
.
11472
×
10
6
Pa
.
keywords:
002
10.0 points
The small piston of a hydraulic lift has a
crosssectional area of 2
.
7 cm
2
and the large
piston has an area of 43 cm
2
, as in the figure
below.
F
2
.
7 cm
2
area
43 cm
2
What force
F
must be applied to the small
piston to maintain the load of 16 kN at a
constant elevation?
Correct answer: 1004
.
65 N.
Explanation:
Let :
A
1
= 2
.
7 cm
2
,
A
2
= 43 cm
2
,
and
W
= 16 kN
.
According to Pascal’s law, the pressure ex
erted on
A
1
must be equal to the one exerted
on
A
2
.
The pressure
P
1
=
F
A
1
must be equal
to the pressure
P
2
=
W
A
2
due to the load.
F
A
1
=
W
A
2
,
so
F
=
A
1
A
2
W
=
(2
.
7 cm
2
)
(43 cm
2
)
(16000 N)
=
1004
.
65 N
.
003
10.0 points
A simple Utube that is open at both ends is
partially filled with a heavy liquid of density
1000 kg
/
m
3
.
A liquid of density 582 kg
/
m
3
is
then poured into one arm of the tube, forming
a column 7
.
7 cm in height, as shown.
h
7
.
7 cm
light liquid
582 kg
/
m
3
heavy liquid
1000 kg
/
m
3
What is the difference in the heights of the
two liquid surfaces?
Correct answer: 3
.
2186 cm.
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alexander (jra2623) – homework 25 – Turner – (92510)
2
Explanation:
Let :
ℓ
= 7
.
7 cm
,
ρ
ℓ
= 582 kg
/
m
3
,
and
ρ
h
= 1000 kg
/
m
3
.
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 Summer '08
 Kaplunovsky
 Work, Correct Answer, Kilogram, Alexander

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