fullwood (tf5349) – Homework # 3 Motion – Catala – (49033)
1
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printout
should
have
20
questions.
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before answering.
001
(part 1 of 2) 10.0 points
A car with an initial speed of 21.1 km/h ac
celerates at a uniform rate of 0.88 m/s
2
for 4.7
s.
Find the final speed of the car.
Correct answer: 9
.
99711 m
/
s.
Explanation:
Let :
v
i
= 21
.
1 km
/
h
,
a
= 0
.
88 m
/
s
2
and
Δ
t
= 4
.
7 s
.
v
f
=
v
i
+
a
Δ
t
= (21
.
1 km
/
h)
·
1000 m
1 km
·
1 h
3600 s
+ (0
.
88 m
/
s
2
)(4
.
7 s)
= 9
.
99711 m
/
s
002
(part 2 of 2) 10.0 points
Find the displacement of the car after that
time.
Correct answer: 0
.
0372668 km.
Explanation:
Δ
x
=
v
i
Δ
t
+
1
2
a
(Δ
t
)
2
= (21
.
1 km
/
h)(4
.
7 s)
·
1 h
3600 s
+
1
2
(
0
.
88 m
/
s
2
)
(4
.
7 s)
2
1 km
1000 m
= 0
.
0372668 km
003
10.0 points
When the shuttle bus comes to a sudden stop
to avoid hitting a dog, it decelerates uniformly
at 5.4 m/s
2
as it slows from 9.4 m/s to 0 m/s.
Find the time interval of acceleration for
the bus.
Correct answer: 1
.
74074 s.
Explanation:
Let :
a
avg
=

5
.
4 m
/
s
2
,
v
i
= 9
.
4 m
/
s
,
and
v
f
= 0 m
/
s
.
a
avg
=
Δ
v
Δ
t
=
v
f

v
0
Δ
t
=

v
0
Δ
t
Δ
t
=

v
i
a
avg
=

9
.
4 m
/
s

5
.
4 m
/
s
2
=
1
.
74074 s
.
004
10.0 points
A worker drops a wrench from the top of a
tower 61.0 m tall.
What
is
the
velocity when
the
wrench
strikes the ground?
Correct answer:

34
.
5951 m
/
s.
Explanation:
Basic Concept:
When
v
i
= 0 m/s, the
equation simplifies to
v
2
f
= 2
a
Δ
y
Given:
v
i
= 0 m
/
s
Δ
y
=

61
.
0 m
a
=

9
.
81 m
/
s
2
Solution:
v
f
=
±
radicalbig
2
a
Δ
y
=
±
radicalBig
2(

9
.
81 m
/
s
2
)(

61 m)
=
±
34
.
5951 m
/
s
Since the wrench is moving downwards,
v
f
=

34
.
5951 m
/
s.
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fullwood (tf5349) – Homework # 3 Motion – Catala – (49033)
2
005
10.0 points
A baby sitter pushing a stroller starts from
rest and accelerates uniformly at a rate of
0.657 m/s
2
.
What is the velocity of the stroller after it
has traveled 7.14 m?
Correct answer: 3
.
063 m
/
s.
Explanation:
Let :
a
= 0
.
657 m
/
s
2
,
Δ
x
= 7
.
14 m
and
v
i
= 0 m
/
s
.
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 Spring '10
 PRO.KIROSHIMA
 Acceleration, Work, Velocity, Correct Answer, m/s, race car

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