Version 151 – Exam 1 – chelikowsky – (59005)
1
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printout
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have
25
questions.
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before answering.
001
10.0 points
The graph shows position as a function of
time for two trains running on parallel tracks.
At time
t
= 0 the position of both trains is 0
(at the origin).
position
time
t
B
B
A
Which is true?
1.
Both trains have the same velocity at
some time before
t
B
.
correct
2.
Both trains speed up all the time.
3.
In the time interval from
t
= 0 to
t
=
t
B
,
train B covers more distance than train A.
4.
Somewhere before time
t
B
, both trains
have the same acceleration.
5.
At time
t
B
, both trains have the same
velocity.
Explanation:
The slope of the curve B is parallel to line
A at some point
t < t
B
.
002
10.0 points
You and your friend throw balloons filled with
water from the roof of a several story apart
ment house. You simply drop a balloon from
rest.
A second balloon is thrown downward
by your friend 3
.
4 s later with an initial speed
of 66
.
64 m
/
s. They hit the ground simultane
ously.
How high is the apartment house?
The
acceleration of gravity is 9
.
8 m
/
s
2
.
Neglect
air resistance.
1. 63.504
2. 92.7202
3. 150.932
4. 86.436
5. 48.6202
6. 120.062
7. 127.449
8. 159.201
9. 58.3222
10. 44.1
Correct answer: 127
.
449 m.
Explanation:
Δ
t
= 3
.
4 s
,
v
0
= 66
.
64 m
/
s
,
and
g
= 9
.
8 m
/
s
2
.
For balloon 1
y
1
=
1
2
g t
2
1
, and for balloon 2
y
2
=
v
0
t
2
+
g t
2
2
2
.
Balloon 2 is thrown Δ
t
sec
onds after balloon 1 and they hit the ground
at the same time, so
t
1
=
t
2
+ Δ
t
and
y
1
=
y
2
g t
2
1
2
=
v
0
(
t
1
−
Δ
t
) +
g
2
(
t
1
−
Δ
t
)
2
=
v
0
(
t
1
−
Δ
t
)
+
g
2
[
t
2
1
−
2
t
1
Δ
t
+ (Δ
t
)
2
]
(
v
0
−
g
Δ
t
)
t
1
=
v
0
Δ
t
−
g
2
(Δ
t
)
2
t
1
=
v
0
Δ
t
−
g
2
(Δ
t
)
2
v
0
−
g
Δ
t
=
(66
.
64 m
/
s)(3
.
4 s)
−
1
2
(9
.
8 m
/
s
2
)(3
.
4 s)
2
66
.
64 m
/
s
−
(9
.
8 m
/
s
2
) (3
.
4 s)
= 5
.
1 s
,
so the height of the house is
y
=
g t
2
1
2
=
(9
.
8 m
/
s
2
) (5
.
1 s)
2
2
=
127
.
449 m
.
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Version 151 – Exam 1 – chelikowsky – (59005)
2
003
10.0 points
The distance between the sun and the Earth
is about 1
.
5193
×
10
11
m.
Express this distance in kilometers.
1.
1
.
5193
×
10
7
km
2.
1
.
5193
×
10
11
km
3.
1
.
5193
×
10
9
km
4.
None of these
5.
1
.
5193
×
10
8
km
correct
6.
1
.
5193
×
10
10
km
7.
1
.
5193
×
10
6
km
Explanation:
1 km = 1
×
10
3
m
,
so
distance =
(
1
.
5193
×
10
11
m
)
·
1 km
1
×
10
3
m
=
1
.
5193
×
10
8
km
.
004
10.0 points
You can obtain a rough estimate of the size
of a molecule with the following simple exper
iment:
Let a droplet of oil spread out on a
fairly large but smooth water surface. The re
sulting ”oil slick” that forms on the surface of
the water will be approximately one molecule
thick.
Given an oil droplet with a mass of 8
.
41
×
10
−
7
kg and a density of 946 kg
/
m
3
that
spreads out to form a circle with a radius of
44
.
4 cm on the water surface, what is the
approximate diameter of an oil molecule?
1. 1.54414e09
2. 1.43545e09
3. 1.90383e09
4. 2.05891e09
5. 1.28881e09
6. 1.56904e09
7. 2.02061e09
8. 1.51011e09
9. 1.67256e09
10. 1.64264e09
Correct answer: 1
.
43545
×
10
−
9
m.
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 Fall '09
 Chelikowsky
 Acceleration, Velocity, Correct Answer, m/s, θ α

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