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CHAPTER
2
KINEMATICS IN
ONE DIMENSION
ANSWERS TO FOCUS ON CONCEPTS QUESTIONS
1.
(b)
Displacement, being a vector, conveys information about magnitude and direction.
Distance conveys no information about direction and, hence, is not a vector.
3.
(c)
The average speed is the distance of 16.0 km divided by the elapsed time of 2.0 h.
The
average velocity is the displacement of 0 km divided by the elapsed time.
The displacement
is 0 km, because the jogger begins and ends at the same place.
6.
(c)
The average acceleration is the change in velocity (final velocity minus initial velocity)
divided by the elapsed time.
The change in velocity has a magnitude of 15.0 km/h.
Since the
change in velocity points due east, the direction of the average acceleration is also due east.
10. (c)
The equations of kinematics can be used only when the acceleration remains constant
and cannot be used when it changes from moment to moment.
13. (d)
According to one of the equation of kinematics
( )
2
1
00
2
, with
0 m/s
xv
t a
t
v
=+
=
, the
displacement is proportional to the acceleration.
19. (b)
Freefall is the motion that occurs while the acceleration is solely the acceleration due to
gravity.
While the rocket is picking up speed in the upward direction, the acceleration is not
just due to gravity, but is due to the combined effect of gravity and the engines.
In fact, the
effect of the engines is greater than the effect of gravity.
Only when the engines shut down
does the freefall motion begin.
24. (a)
The slope of the line in a position versus time graph gives the velocity of the motion.
The slope for part A is positive.
For part B the slope is negative.
For part C the slope is
positive.
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View Full DocumentChapter 2
Problems
45
CHAPTER
2
KINEMATICS IN
ONE DIMENSION
PROBLEMS
______________________________________________________________________________
8.
REASONING
The younger (and faster) runner should start the race after the older runner,
the delay being the difference between the time required for the older runner to complete the
race and that for the younger runner. The time for each runner to complete the race is equal
to the distance of the race divided by the average speed of that runner (see Equation 2.1).
SOLUTION
The difference between the times for the two runners to complete the race is
, where
50
18
tt
−
()
50
18
50yrold
18yrold
Distance
Distance
and
Average Speed
Average Speed
==
(2.1)
The difference between these two times (which is how much later the younger runner should
start) is
50
18
50yrold
18yrold
33
Distance
Distance
Average Speed
Average Speed
10.0 10 m
64 s
4.27 m/s
4.39 m/s
−=
−
××
=−=
______________________________________________________________________________
12.
REASONING
The definition of average velocity is given by Equation 2.2 as
Average velocity = Displacement/(Elapsed time). The displacement in this expression is the
total displacement, which is the sum of the displacements for each part of the trip.
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 Spring '08
 CROFT
 Physics

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