CHAPTER
2
KINEMATICS IN
ONE DIMENSION
CONCEPTUAL QUESTIONS
____________________________________________________________________________________________
1.
REASONING AND SOLUTION
The displacement of the honeybee for the trip is
not
the
same as the distance traveled by the honeybee. As stated in the question, the distance
traveled by the honeybee is 2 km. The displacement for the trip is the shortest distance
between the initial and final positions of the honeybee. Since the honeybee returns to the
hive, its initial position and final position are the same; therefore, the displacement of the
honeybee is zero.
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2.
REASONING AND SOLUTION
The buses
do not
have equal velocities. Velocity is a
vector, with both magnitude and direction. In order for two vectors to be equal, they must
have the same magnitude and the same direction. The direction of the velocity of each bus
points in the direction of motion of the bus. Thus, the directions of the velocities of the
buses are different. Therefore, the velocities are not equal, even though the speeds are the
same.
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3.
REASONING AND SOLUTION
The average speed of a vehicle is defined as the total
distance covered by the vehicle divided by the time required for the vehicle to cover the
distance.
Both distance and time are scalar quantities.
Since the average speed is the ratio
of two scalar quantities, it is a scalar quantity.
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4.
SSM
REASONING AND SOLUTION
Consider the four traffic lights
1
,
2
,
3
and
4
shown below.
Let the distance between lights
1
and
2
be
x
12
, the distance between lights
2
and
3
be
x
23
, and the distance between lights
3
and
4
be
x
34
.
v
x
12
x
34
x
23
1
2
3
4
The lights can be timed so that if a car travels with a constant speed
v
, red lights can be
avoided in the following way.
Suppose that at time
t
= 0 s, light
1
turns green while the rest
are red.
Light
2
must then turn green in a time
t
12
,
where
t
12
=
x
12
/
v
.
Light
3
must turn
green in a time
t
23
after light
2
turns green, where
t
23
=
x
23
/
v
.
Likewise, light
4
must turn
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45
KINEMATICS IN ONE DIMENSION
green in a time
t
34
after light
3
turns green, where
t
34
=
x
34
/
v
.
Note that the timing of traffic
lights is more complicated than indicated here when groups of cars are stopped at light
1.
Then the acceleration of the cars, the reaction time of the drivers, and other factors must be
considered.
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5.
REASONING AND SOLUTION
The velocity of the car is a vector quantity with both
magnitude and direction
The speed of the car is a scalar quantity and has nothing to do with
direction. It is possible for a car to drive around a track at constant speed. As the car drives
around the track, however, the car must change direction. Therefore, the direction of the
velocity
changes
, and the velocity cannot be constant.
The
incorrect
statement is (a).
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6.
REASONING AND SOLUTION
Answers will vary. One example is a ball that is thrown
straight up in the air. When the ball is at its highest point, its velocity is momentarily zero.
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 Fall '07
 Baskins
 Velocity, m/s

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