Unit 3 Review Answers
(Student textbook pages 268–271)
Visualizing Key Ideas
1. Vector quantities: displacement, position, velocity,
acceleration
Scalar quantities: distance, speed, time
Types of speeds and velocities: constant, changing,
average, instantaneous
Slopes on a position-time graph: positive, negative, zero
Checking Concepts
2. a reference point
15. Sample answer: You feel a change in motion, or
acceleration when you experience a change in your
velocity. When you feel a change in motion, you are
actually feeling the force that is causing this change. Your
body tries to resist this change as you continue to move
in the direction you were moving.
16. 0.02 m/s2[W]
17. Because negative acceleration is changing the velocity
to a more negative value (or less positive value), the line
on the position-time graph will be curved such that the
slopes along the curve are decreasing in value.
3. Displacement is found by taking the position of the final
point on the number line and subtracting the position
of the initial point. The direction will be indicated by the
sign of the answer.
4. The choice of the reference point has no effect on the
18. The graph will be a straight sloping line segment with a
negative slope.
19. (a) when distance and magnitude of displacement are
equal (i.e., a straight road or path)
(b) any distance travelled where there is a change in
direction that would cause the magnitude of the
displacement to be less than the distance travelled
displacement. The displacement is a vector between the
two points (and this vector is the same, regardless of the
choice of reference point for the two positions).
5. Sample answers: scalar: time, temperature, mass,
distance, speed; vectors: force, velocity, displacement,
acceleration, weight, position
(c) this scenario can never occur
20.
Velocity-Time
6. Sample answer: constant speed: running around a track
7. 136 s
8. Average speed and instantaneous speed are equal when
the object is travelling at a constant speed.
9. about 20 min
10. This statement is false, because the direction will be
opposite. The correct statement would be: You throw a
ball upwards at 5.0 m/s. When it gets back to your hand,
the magnitude of the velocity will be the same, but the
direction will be opposite.
11. the speed changes, the speed remains constant, but the
direction changes, and the speed and direction change
12. Sample answers: speed changes: A ball is dropped from
a height of 10 m; direction changes: a person sitting on a
Ferris wheel; speed and direction change: a ball is kicked
through the air
16.0
14.0
Velocity (m/s[S])
at 4.0 m/s; changing speed: the initial part of a 100 m
sprint, when the runners cover a greater distance over
each consecutive time interval
12.0
10.0
8.0
6.0
4.0
2.0
0.0
0
5
10
15
20
25
30
Time (s)
Students’ stories should match the velocity and time
values on the graph.
21. about 13 km
Understanding Key Ideas
22. (a) 8 m south
(b) 8 m north
13. The slope of the line between two points on a position-
23. Sample answer: A car moving north at 75 km/h is
14. Regina is incorrect, because speed is a scalar and
24. The line on a position-time graph is straight for uniform
time graph is the average velocity of the object during
that time interval.
acceleration is a vector. Acceleration is the change in
velocity during a specific time interval.
uniform motion and a car increasing speed after a red
light turns green is non-uniform motion.
motion. The graph is not straight on a position-time
graph when the motion is not uniform.
25. (a) 27.1 km[W]
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(b) 4 km[S]
t  8 s the velocity is zero, in the interval from t  8 s to
t  12 s, the velocity is 3 m/s[E] and in the interval
t  12 s to t  21 s, the velocity is 4 m/s[W].
(c) 12.7 km[W]
26. (a) 471 m
36. (a) 3.1 m/s[E]
(b) 0 m
(b) 0 m/s
(c) these answers are not the same, because displacement
is the difference between start position and end
position. Because she ended up where she started, the
displacement is zero. However, she did move, so she
did cover distance (a scalar quantity).
(c) 2.3 m/s[W]
37. (a) from 0 to 5 seconds the object was moving the fastest
(b) the object was travelling east when it was moving the
(b) the object is not moving
fastest
(c) average speed  3.5 m/s and average velocity  0
38. 513 m[W]
(c) the object is travelling north
39. 6.1  102 m[E]
27. (a) the object is travelling south
28. 8.5 km
40. 6.9 m/s2[forward]
29. The object is speeding up if the gaps between the dots
41. (a)
Velocity-Time
16
Velocity (m/s)[forward]
are increasing, the object is slowing down if the dots
are getting closer together, and the object is staying at a
constant velocity if the dots are the same distance apart.
30. Average speed is calculated by connecting the points
of interest with a straight line, and then calculating the
slope of the line.
31. 3 m/s
32.
Distance-Time
14
12
10
8
6
4
2
0
30.0
Distance (m)
25.0
2
4
6
8
10 12 14 16 18 20
Time (s)
Distance (m) Olivia
20.0
(b) 225 m[forward]
42.
15.0
10.0
Position-Time
Distance (m) Randy
16
10.0
20.0
30.0
40.0
50.0
60.0
Time (s)
(a) Olivia has the higher average speed over the first
30.0 seconds. Her average speed is 0.5 m/s and Randy
has an average speed of just 0.35 m/s.
(b) Olivia would be 72 m in front. Olivia would have
moved 240 m while Randy would have moved 168 m
in the 8 minutes. 240  168  72 m
33. You would need a speedometre to determine the
magnitude of the instantaneous velocity, and you would
need a compass to determine the direction of motion.
34. The area between the time axis and the graph is
calculated to find the displacement of the object.
35. In the first interval from t  0 to t  5 seconds, the
velocity is 5 m/s[E], in the interval from t  5 s to
Position (m)[forward]
5.0
0.0
0.0
0
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
Time (s)
43. The strip should show dots close together, but getting
farther apart while the object has positive acceleration.
In the next section of the strip, the dots should be evenly
spaced while the object has no acceleration (constant
velocity). In the last section of the strip, the dots should
get closer together when the object is experiencing
negative acceleration.
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44. (a) 74 km/h[W]
(b) It must be assumed that the road is straight and that
the signs were giving true positions and not just
distances.
(c) You would only have been able to calculate average
speed, not average velocity.
45. 6.5 m/s[N]
46. (a) The alligator has a greater speed, so the alligator
would win.
(b) When the alligator crossed the finish line, the
Olympic sprinter would be 17.1 m behind.
(c) It must be assumed that they are both at their
maximum speed throughout the race, and that each
can maintain their maximum speed for the entire
race.
47. (a) 15 m/s
(b) The magnitude of the velocity cannot be larger than
the speed in any situation.
(c) The instantaneous speed can be larger than the
average speed in the interval, just as it could also be
smaller than the average speed. The average speed is
just the average, so values in the interval can be larger
or smaller than the average for periods of time within
the interval.
48. 5.8 s
49. 2.5 m/s or  3 m/s
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