louey (cal2859) – Ch4HW2 – florin – (56930)
1
This
printout
should
have
12
questions.
Multiplechoice questions may continue on
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before answering.
001
10.0points
If a chain of 40 identical short springs linked
end to end has a stiffness of 200 N
/
m, what is
the stiffness of one short spring?
Correct answer: 8000 N
/
m.
Explanation:
Springs in series have the effective stiffness
K
, where
K
is given in terms of the stiffnesses
of the individual springs as follows:
1
/K
= 1
/k
1
+ 1
/k
2
+
···
+ 1
/k
N
.
For identical springs, we have
k
=
NK
, where
k
is the stiffness of a single spring. Therefore
k
= (40)(200 N
/
m)
=
8000 N
/
m
.
002
10.0points
You place 45 identical springs side by side (in
parallel) and connect them to a large, massive
block.
The stiffness of the 45spring combi
nation is 20295 N
/
m. What is the stiffness of
one of the individual springs?
Correct answer: 451 N
/
m.
Explanation:
Springs in parallel have an effective stiffness
K
, where
K
is given in terms of the stiffnesses
of the individual springs as follows:
K
=
k
1
+
k
2
+
···
+
k
N
.
For identical springs, we have
K
=
Nk
, or
k
=
K/N
, where
k
is the stiffness of a single
spring.
Therefore,
k
=
20295 N
/
m
45
=
451 N
/
m
.
003(part1of4)10.0points
One mole of tungsten (6
.
02
×
10
23
atoms)
has
a
mass
of 184
g,
and
its density
is
19
.
3 g
/
cm
3
, so the centertocenter distance
between atoms is 2
.
51
×
10

10
m. You have a
long, thin bar of tungsten, 2
.
1 m long, with a
square cross section, 0
.
15 cm on a side. You
hang the rod vertically and attach a 455 kg
mass to the bottom, and you observe that
the bar becomes 1
.
27 cm longer. From these
measurements, it is possible to determine the
stiffness of one interatomic bond in tungsten.
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 Spring '08
 Turner
 Atom, Mole, Correct Answer, rod

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