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reddy (ar38357) – Kinematics B – clancy – (SCI4112)
1
This printout should have 10 questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
beFore answering.
001
10.0 points
An automobile accelerates From rest at
0
.
2 m
/
s
2
For 21 s. The speed is then held
constant For 17 s, aFter which there is an ac
celeration oF

1
.
5 m
/
s
2
until the automobile
stops.
What total distance was traveled?
Correct answer: 0
.
12138 km.
Explanation:
±or the acceleration,
Let :
v
0
= 0
,
a
1
= 0
.
2 m
/
s
2
,
and
t
1
= 21 s
.
The displacement is
s
1
=
v
0
t
0
+
1
2
a
1
t
2
1
=
1
2
a
1
t
2
1
,
reaching a speed oF
v
1
=
v
0
+
a t
1
=
a
1
t
1
.
±or the constant speed,
Let :
a
2
= 0
and
t
2
= 17 s
.
The displacement is
s
2
=
v
1
t
2
=
a
1
t
1
t
2
,
maintaining a speed oF
v
2
=
v
1
=
a
1
t
1
.
During the braking interval,
Let :
a
3
=

1
.
5 m
/
s
2
and
v
f
= 0
.
v
2
3
=
v
2
2
+ 2
a
3
s
3
= 0
s
3
=

v
2
2
2
a
3
=

(
a
1
t
1
)
2
2
a
3
,
so
s
=
s
1
+
s
2
+
s
3
=
1
2
a
1
t
2
1
+
a
1
t
1
t
2

a
2
1
t
2
2
a
3
=
1
2
(0
.
2 m
/
s
2
) (21 s)
2
+ (0
.
2 m
/
s
2
) (21 s) (17 s)

(0
.
2 m
/
s
2
)
2
(21 s)
2
2 (

1
.
5 m
/
s
2
)
= 121
.
38 m =
0
.
12138 km
.
002
10.0 points
Two students are on a balcony 20
.
9 m above
the street. One student throws a ball ver
tically downward at 14
.
2 m
/
s; at the same
instant, the other student throws a ball verti
cally upward at the same speed. The second
ball just misses the balcony on the way down.
How Far apart are the balls 0
.
48 s aFter they
are thrown? The acceleration oF gravity is
9
.
8 m
/
s
2
.
Correct answer: 13
.
632 m.
Explanation:
Let :
h
= 20
.
9 m
,
v
i,
1
= 14
.
2 m
/
s
,
v
i,
2
=

14
.
2 m
/
s
,
Δ
t
= 0
.
48 s
,
and
g
= 9
.
8 m
/
s
2
.
±or the frst ball,
Δ
y
1
=
v
i,
1
Δ
t

1
2
g
(Δ
t
)
2
= (

14
.
2 m
/
s) (0
.
48 s)

1
2
(
9
.
8 m
/
s
2
)
(0
.
48 s)
2
=

7
.
94496 m
which is 7
.
94496 m below the balcony.
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This note was uploaded on 11/21/2010 for the course PHYS 12231 taught by Professor Sontar during the Fall '10 term at Ill. Chicago.
 Fall '10
 Sontar
 Physics

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