hiarker (srh959) – homework 05 – Turner – (58220)
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001
(part 1 of 3) 10.0 points
Two cars are traveling along a straight line in
the same direction, the lead car at 34 m
/
s and
the other car at 46 m
/
s. At the moment the
cars are 56 m apart, the lead driver applies the
brakes, causing the car to have an acceleration
of
−
2
.
4 m/s
2
.
a) How long does it take for the lead car to
stop?
Correct answer: 14
.
1667 s.
Explanation:
Basic Concept:
a
avg
=
v
f
−
v
i
Δ
t
=
−
v
i
Δ
t
since
v
f
= 0 m/s.
Given:
v
i,
1
= +34 m
/
s
v
f,
1
= 0 m
/
s
a
1
=
−
2
.
4 m
/
s
2
Solution:
Δ
t
1
=
−
v
i,
1
a
1
=
−
34 m
/
s
−
2
.
4 m
/
s
2
= 14
.
1667 s
002
(part 2 of 3) 10.0 points
Assume that the driver of the chasing car
applies the brakes at the same time as the
driver of the lead car.
b) What must the chasing car’s minimum
negative acceleration be to avoid hitting the
lead car?
Correct answer:
−
3
.
56429 m
/
s
2
.
Explanation:
Basic Concepts:
The equations simplify
to
Δ
x
=
1
2
(
v
f
+
v
i
)
Δ
t
=
v
i
2
Δ
t
and
0 =
v
2
i
+ 2
a
Δ
x
since
v
f
= 0 m/s.
Given:
v
i,
2
= +46 m
/
s
v
f,
2
= 0 m
/
s
Δ
x
2
= Δ
x
1
+ 56 m
Δ
t
2
= Δ
t
1
= 14
.
1667 s
Solution:
The lead car traveled
Δ
x
1
=
34 m
/
s
2
(14
.
1667 s) = 240
.
833 m
The chasing car traveled
Δ
x
2
= 240
.
833 m + 56 m = 296
.
833 m
with a minimum acceleration of
a
2
=
−
v
2
i,
2
2Δ
x
2
=
−
(46 m
/
s)
2
2(296
.
833 m)
=
−
3
.
56429 m
/
s
2
003
(part 3 of 3) 10.0 points
c) How long does it take the chasing car to
stop?
Correct answer: 12
.
9058 s.
Explanation:
Basic Concepts:
a
=
v
f
−
v
i
Δ
t
=
−
v
i
Δ
t
since
v
f
= 0 m/s.
Given:
v
i,
2
= 46 m
/
s
a
2
=
−
3
.
56429 m
/
s
2
Solution:
Δ
t
2
=
−
v
i,
2
a
2
=
−
46 m
/
s
−
3
.
56429 m
/
s
2
= 12
.
9058 s
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hiarker (srh959) – homework 05 – Turner – (58220)
2
004
(part 1 of 2) 10.0 points
Throw a ball upward from point
O
with an
initial speed of 86 m
/
s.
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 Spring '09
 NUI
 Physics, Acceleration, Work, Correct Answer, m/s, patrol car

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