44
Motion in One Dimension
P2.56
a
dv
dt
v
=
=
−
3 00
2
.
,
v
i
=
1 50
.
m s
Solving for
v
,
dv
dt
v
=
−
3 00
2
.
v
dv
dt
v
v
t
t
v
v
v
v
v
t
t
i
i
i
−
=
=
z
z
= −
−
+
= −
=
−
2
0
3 00
1
1
3 00
3 00
1
1
.
.
.
.
or
When
v
v
i
=
2
,
t
v
i
=
=
1
3 00
0 222
.
.
s
.
Additional Problems
*P2.57
The distance the car travels at constant velocity,
v
0
, during the reaction time is
∆
∆
x
v
t
r
a f
1
0
=
. The
time for the car to come to rest, from initial velocity
v
0
, after the brakes are applied is
t
v
v
a
v
a
v
a
f
i
2
0
0
0
=
−
=
−
=
−
and the distance traveled during this braking period is
∆
x
vt
v
v
t
v
v
a
v
a
f
i
a f
2
2
2
0
0
0
2
2
0
2
2
=
=
+
F
H
G
I
K
J
=
+
F
H
G
I
K
J
−
F
H
G
I
K
J
= −
.
Thus, the total distance traveled before coming to a stop is
s
x
x
v
t
v
a
r
stop
=
+
=
−
∆
∆
∆
a f
a f
1
2
0
0
2
2
.
*P2.58
(a)
If a car is a distance
s
v
t
v
a
r
stop
=
−
0
0
2
2
∆
(See the solution to Problem 2.57) from the
intersection of length
s
i
when the light turns yellow, the distance the car must travel before
the light turns red is
∆
∆
x
s
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 Fall '11
 Staff
 Physics, 1 km, Automobile, Brake, 1.50 M, 0.278 M

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