printout
should
have
12
questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
beFore answering.
001
(part 1 oF 2) 10.0 points
The velocity
v
(
t
) oF some particle is plotted
as a Function oF time on the graph below.
The scale on the horizontal axis is 5 s per
division and on the vertical axis 1 m
/
s per
division.
0
1
2
3
4
5
6
0
1
2
3
4
5
6
7
8
9
v
(
t
)
time (
×
5 s)
velocity(
×
1m
/
s)
Initially, at
t
= 0 the particle is at
x
0
=
31 m. What is the position
x
oF the particle
at time
t
= 20 s?
Correct answer: 81 m.
Explanation:
Looking at the
v
(
t
) plot we see that over
time
t
= 4
×
5 s = 20 s, the particle’s velocity
decreases From the initial
v
0
= 4
×
1 m
/
s =
4 m
/
s to fnal
v
f
= 1
×
1 m
/
s = 1 m
/
s
.
The
v
(
t
) line is straight, which indicates constant
deceleration rate, hence the average velocity
is given by
¯
v
=
v
0
+
v
f
2
= 2
.
5 m
/
s
.
Consequently,
the
particle’s
displacement
during this time is simply
Δ
x
=
t
×
¯
v
= 50 m
,
and its fnal position
x
=
x
0
+ Δ
x
=
81 m
.
002
(part 2 oF 2) 10.0 points
What is the particle’s acceleration?
Correct answer:

0
.
15 m
/
s
2
.
Explanation:
The average acceleration oF the particle is
¯
a
=
Δ
v
Δ
t
=
v
f

v
0
t
=

0
.
15 m
/
s
2
.
Since the
v
(
t
) line is straight, the acceleration
is constant, hence
a
= ¯
a
=

0
.
15 m
/
s
2
.
003
(part 1 oF 2) 10.0 points
A speeder passes a parked police car at 33.3
m/s.
Instantaneously, the police car starts
From rest with a uniForm acceleration oF 2.43
m/s
2
.
a) How much time pases beFore the speeder
is overtaken by the police car?
Correct answer: 27
.
4074 s.
Explanation:
Basic Concepts:
±or the speeder,
Δ
x
s
=
v
s
Δ
t
±or the policeman,
v
i
= 0 m/s, so the equa
tion simplifes to
Δ
x
p
=
1
2
a
p
(Δ
t
)
2
Let :
v
s
= 33
.
3 m
/
s
v
i,p
= 0 m
/
s
a
p
= 2
.
43 m
/
s
2
.
Solution:
Δ
x
s
= Δ
x
p
v
s
Δ
t
=
1
2
a
p
(Δ
t
)
2
2
v
s
Δ
t
=
a
p
(Δ
t
)
2
2
v
s
=
a
p
Δ
t
Δ
t
=
2
v
s
a
p
=
2(33
.
3 m
/
s)
2
.
43 m
/
s
2
=
27
.
4074 s
.
oldhomework 04 – Turner – (58185)
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 Fall '08
 Turner
 Acceleration, Work, Correct Answer, police car, patrol car, Hinojosa

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