Version 040 – Quiz 2 – coker – (58245)
1
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printout
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have
24
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
Quiz 2 covers only topics covered in class
lectures over Chs.
6, 7, 8 and 9 in Oha
nian/Markert.
001
10.0 points
A 59 g block is released from rest and slides
down a frictionless track that begins 1
.
9 m
above the horizontal, as shown in the figure.
At the bottom of the track, where the surface
is horizontal, the block strikes and sticks to a
light spring with a spring constant of 13 N
/
m.
The acceleration of gravity is 9
.
8 m
/
s
2
.
1
.
9 m
59 g
13 N
/
m
Find the maximum distance the spring is
compressed.
1. 0.350392
2. 0.206738
3. 0.249837
4. 0.411111
5. 0.217188
6. 0.284493
7. 0.344828
8. 0.306496
9. 0.196167
10. 0.180263
Correct answer: 0
.
411111 m.
Explanation:
Let :
m
= 59 g = 0
.
059 kg
,
h
i
= 1
.
9 m
,
and
k
= 13 N
/
m
.
From conservation of mechanical energy, we
have
m g h
i
=
1
2
k x
2
x
=
radicalbigg
2
m g h
i
k
=
radicalBigg
2 (0
.
059 kg) (9
.
8 m
/
s
2
) (1
.
9 m)
13 N
/
m
=
0
.
411111 m
.
002
10.0 points
For this problem,
we assume that we are
on PlanetI. The
radius of this planet is
R
=2390 km, the gravitational acceleration
at the surface is
g
I
=8
.
35 m
/
s
2
, and the grav
itational constant
G
= 6
.
67
×
10
−
11
N m
2
/kg
2
in SI units. The mass of PlanetI is not given.
Not all the quantities given here will be used.
Suppose a cannon ball of mass
m
= 5090 kg
is projected vertically upward from the sur
face of this planet.
It rises to a maximum
height
h
=7600
.
2 km above the surface of the
planet.
Caution: Here the gravitational accelera
tion decreases as the cannon ball travels away
from PlanetI.
R
h
Determine the kinetic energy (in Joules) of
the cannon ball immediately after it is fired
off.
1. 28675000000.0
2. 93699500000.0
3. 77277500000.0
4. 99814500000.0
5. 24246500000.0
6. 171427000000.0
7. 64253700000.0
8. 55935700000.0
9. 105450000000.0
10. 96064400000.0
Correct answer: 7
.
72775
×
10
10
J.
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Version 040 – Quiz 2 – coker – (58245)
2
Explanation:
For
r > R
, the potential energy of the
cannon ball is
U
=
−
G M m
r
.
Since
g
I
=
G M
R
2
,
U
=
−
m g
I
R
2
r
. Apply conservation of
energy:
E
=
K
i
+
U
i
=
K
f
+
U
f
⇒
K
i
=
U
f
−
U
i
=
−
mg
I
R
2
/r
−
(
−
mg
I
R
) =
mg
I
R
(1
−
R/r
), where
r
=
R
+
h
.
003
10.0 points
How does the force of gravity between two
bodies change when the distance between
them doubles?
1.
Unable
to
determine;
the
mass
is
needed.
2.
halves
3.
quadruples
4.
drops to one quarter of its original value
correct
5.
remains the same
6.
doubles
Explanation:
The force of gravity between two bodies
is inversely proportional to the square of the
distance separating them
parenleftbigg
F
∝
1
r
2
parenrightbigg
, so the
force of gravity will be
F
′
∝
1
(2
r
)
2
=
1
4
1
r
2
∝
1
4
F ,
i.e.
, one fourth of its original value.
004
(part 1 of 2) 10.0 points
Consider a force of 73
.
6 N, pulling 3 blocks of
identical masses, where each mass is 0
.
9 kg,
along a rough horizontal surface.
The coef
ficient of kinetic friction between the blocks
and the surface is given by 0
.
6. The accelera
tion of the blocks is
a
.
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 Spring '08
 Turner
 Physics, Force, Friction, Correct Answer

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