le (txl65) – FluidI – mohanty – (81440)
1
This printout should have 15 questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
be±ore answering.
001 (part 1 of 2) 10.0 points
In a 56 s interval, 719 hailstones strike a glass
window o± area 0
.
787 m
2
at an angle 61
◦
to the
window sur±ace. Each hailstone has a mass o±
7 g and speed o± 7
.
9 m
/
s.
I± the collisions are elastic, fnd the average
±orce on the window.
Correct answer: 1
.
24198 N.
Explanation:
Let :
t
= 56 s
,
N
= 719
,
θ
= 61
◦
,
v
= 7
.
9 m
/
s
,
and
m
= 7 g = 0
.
007 kg
.
The ±orce is
F
=
m
Δ
v
Δ
t
=
m
2
v N
sin
θ
t
= (0
.
007 kg)
2 (7
.
9 m
/
s) (719) sin 61
◦
56 s
=
1
.
24198 N
.
002 (part 2 of 2) 10.0 points
Find the pressure on the window.
Correct answer: 1
.
57812 N
/
m
2
.
Explanation:
Let :
A
= 0
.
787 m
2
.
The pressure is given by
P
=
F
A
=
1
.
24198 N
0
.
787 m
2
=
1
.
57812 N
/
m
2
.
003 (part 1 of 2) 10.0 points
In a car li±t used in a service station, com
pressed air exerts a ±orce on a small piston
o± circular crosssection having a radius o±
4
.
01 cm. This pressure is transmitted by a
liquid to a second piston o± radius 17
.
1 cm.
What ±orce must the compressed air exert
in order to li±t a car weighing 13900 N?
Correct answer: 764
.
384 N.
Explanation:
Let :
r
1
= 4
.
01 cm
,
r
2
= 17
.
1 cm
,
and
F
2
= 13900 N
.
Because the pressure exerted by the
compressed air is transmitted undiminished
throughout the ²uid, we have
F
1
A
1
=
F
2
A
2
F
1
=
p
A
1
A
2
P
F
2
=
p
π r
2
1
π r
2
2
P
F
2
=
π
(4
.
01 cm)
2
π
(17
.
1 cm)
2
(13900 N)
=
764
.
384 N
.
004 (part 2 of 2) 10.0 points
What air pressure will produce this ±orce?
Correct answer: 1
.
51312
×
10
5
Pa.
Explanation:
P
=
F
1
A
1
=
F
1
π r
2
1
=
764
.
384 N
π
(17
.
1 cm)
2
·
p
100 cm
1 m
P
2
=
1
.
51312
×
10
5
Pa
.
005
10.0 points
A 84
.
1 kg solid cylinder, 2
.
49 m long and with
an end radius o± 3
.
9 cm, stands on one end.
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 Spring '11
 sdsd
 Pressure measurement

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