Answer Key
Velocity is Defined As
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University:
Kentucky State University -
Course:
PHY 211 | General Physics I Academic year:
2021
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Views:
159
Pages:
13
Author:
gaarmaakbn9h
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
1. Velocity is defined as:
A. rate of change of position with time
B. position divided by time
C. rate of change of acceleration with time
D. a speeding up or slowing down
E. change of position
ans: A
2. Acceleration is defined as:
A. rate of change of position with time
B. speed divided by time
C. rate of change of velocity with time
D. a speeding up or slowing down
E. change of velocity
ans: C
3. Which of the following is a scalar quantity?
A. Speed
B. Velocity
C. Displacement
D. Acceleration
E. None of these
ans: A
4. Which of the following is a vector quantity?
A. Mass
B. Density
C. Speed
D. Temperature
E. None of these
ans: E
5. Which of the following is NOT an example of accelerated motion?
A. Vertical component of projectile motion
B. Circular motion at constant speed
C. A swinging pendulum
D. Earth’s motion about sun
E. Horizontal component of projectile motion
ans: E
36
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS 6. A particle goes from x = −2 m, y = 3 m, z = 1 m to x = 3 m, y = −1 m, z = 4 m. Its
displacement is:
A. (1 m) î + (2 m) ĵ + (5 m) k̂
B. (5 m) î − (4 m) ĵ + (3 m) k̂
C. −(5 m) î + (4 m) ĵ − (3 m) k̂
D. −(1 m) î − (2 m) ĵ − (5 m) k̂
E. −(5 m) î − (2 m) ĵ + (3 m) k̂
ans: B
7. A jet plane in straight horizontal flight passes over your head. When it is directly above you,
the sound seems to come from a point behind the plane in a direction 30◦ from the vertical.
The speed of the plane is:
A. the same as the speed of sound
B. half the speed of sound
C. three-fifths the speed of sound
D. 0.866 times the speed of sound
E. twice the speed of sound
ans: B
8. A plane traveling north at 200 m/s turns and then travels south at 200 m/s. The change in its
velocity is:
A. zero
B. 200 m/s north
C. 200 m/s south
D. 400 m/s north
E. 400 m/s south
ans: E
9. Two bodies are falling with negligible air resistance, side by side, above a horizontal plane. If
one of the bodies is given an additional horizontal acceleration during its descent, it:
A. strikes the plane at the same time as the other body
B. strikes the plane earlier than the other body
C. has the vertical component of its velocity altered
D. has the vertical component of its acceleration altered
E. follows a straight line path along the resultant acceleration vector
ans: A
10. The velocity of a projectile equals its initial velocity added to:
A. a constant horizontal velocity
B. a constant vertical velocity
C. a constantly increasing horizontal velocity
D. a constantly increasing downward velocity
E. a constant velocity directed at the target
ans: D
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
37 11. A stone thrown from the top of a tall building follows a path that is:
A. circular
B. made of two straight line segments
C. hyperbolic
D. parabolic
E. a straight line
ans: D
12. Identical guns fire identical bullets horizontally at the same speed from the same height above
level planes, one on the Earth and one on the Moon. Which of the following three statements
is/are true?
I. The horizontal distance traveled by the bullet is greater for the Moon.
II. The flight time is less for the bullet on the Earth.
III. The velocity of the bullets at impact are the same.
A. III only
B. I and II only
C. I and III only
D. II and III only
E. I, II, III
ans: B
13. A stone is thrown horizontally and follows the path XYZ shown. The direction of the acceleration of the stone at point Y is:
•........................................................
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X
.......
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•....................
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Y ......................
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horizontal
Z •
A. ↓
B. →
C.
D.
E.
ans: A
38
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS 14. A bullet shot horizontally from a gun:
A. strikes the ground much later than one dropped vertically from the same point at the same
instant
B. never strikes the ground
C. strikes the ground at approximately the same time as one dropped vertically from the same
point at the same instant
D. travels in a straight line
E. strikes the ground much sooner than one dropped from the same point at the same instant
ans: C
15. A bomber flying in level flight with constant velocity releases a bomb before it is over the
target. Neglecting air resistance, which one of the following is NOT true?
A. The bomber is over the target when the bomb strikes
B. The acceleration of the bomb is constant
C. The horizontal velocity of the plane equals the vertical velocity of the bomb when it hits
the target
D. The bomb travels in a curved path
E. The time of flight of the bomb is independent of the horizontal speed of the plane
ans: C
16. The airplane shown is in level flight at an altitude of 0.50 km and a speed of 150 km/h. At
what distance d should it release a heavy bomb to hit the target X? Take g = 10 m/s2 .
.......
... .......
... ....................................................
...
.
.............................................
...................................................
..............
↑
|
|
|
0.5 km
|
|
|
↓
... ... ... ... ...
150 km/h
...................................................
X
•
←−−−−−−−− d −−−−−−−−→
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
A.
B.
C.
D.
E.
150 m
295 m
420 m
2550 m
15, 000 m
ans: C
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
39 17. An object is shot from the back of a railroad flatcar moving at 40 km/h on a straight horizontal
road. The launcher is aimed upward, perpendicular to the bed of the flatcar. The object falls:
A. in front of the flatcar
B. behind the flatcar
C. on the flatcar
D. either behind or in front of the flatcar, depending on the initial speed of the object
E. to the side of the flatcar
ans: C
18. A ball is thrown horizontally from the top of a 20-m high hill. It strikes the ground at an angle
of 45◦ . With what speed was it thrown?
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20 m
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45
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↓ ...................................................................................................................
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A.
B.
C.
D.
E.
14 m/s
20 m/s
28 m/s
32 m/s
40 m/s
ans: B
19. A stone is thrown outward from the top of a 59.4-m high cliff with an upward velocity component of 19.5 m/s. How long is stone in the air?
A. 4.00 s
B. 5.00 s
C. 6.00 s
D. 7.00 s
E. 8.00 s
ans: C
20. A large cannon is fired from ground level over level ground at an angle of 30◦ above the
horizontal. The muzzle speed is 980 m/s. Neglecting air resistance, the projectile will travel
what horizontal distance before striking the ground?
A. 4.3 km
B. 8.5 km
C. 43 km
D. 85 km
E. 170 km
ans: D
40
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS 21. A boy on the edge of a vertical cliff 20 m high throws a stone horizontally outward with a speed
of 20 m/s. It strikes the ground at what horizontal distance from the foot of the cliff? Use
2
g = 10 m/s .
A. 10 m
B. 40 m
C. 50√
m
D. 50 5 m
E. none of these
ans: B
22. Which of the curves on the graph below best represents the vertical component vy of the
velocity versus the time t for a projectile fired at an angle of 45◦ above the horizontal?
............... F
vy
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A ....................................................................... B
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.................. E
D
A.
B.
C.
D.
E.
OC
DE
AB
AE
AF
ans: D
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
41 23. A cannon fires a projectile as shown. The dashed line shows the trajectory in the absence of
gravity; points MNOP correspond to the position of the projectile at one second intervals. If
2
g = 10 m/s , the lengths X,Y,Z are:
.
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Y
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M
•
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A.
B.
C.
D.
E.
•X
•
N
O
Z
•
P
5 m, 10 m, 15 m
5 m, 20 m, 45 m
10 m, 40 m, 90 m
10 m, 20 m, 30 m
0.2 m, 0.8 m, 1.8 m
ans: B
24. A dart is thrown horizontally toward X at 20 m/s as shown. It hits Y 0.1 s later. The distance
XY is:
.........
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•••••••••••
•••• ••••••
•
••
•
•• ••••••••••••• ••••
•
• • • ••
•••• ••• • ••• •••
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••• ••• •• ••
••• •••••• ••
•••
••••• •••••••
••••••••
•
A.
B.
C.
D.
E.
42
2m
1m
0.5 m
0.1 m
0.05 m
ans: E
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
X
Y 25. A projectile is fired from ground level over level ground with an initial velocity that has a
2
vertical component of 20 m/s and a horizontal component of 30 m/s. Using g = 10 m/s , the
distance from launching to landing points is:
A. 40 m
B. 60 m
C. 80 m
D. 120 m
E. 180 m
ans: D
26. An object, tied to a string, moves in a circle at constant speed on a horizontal surface as shown.
The direction of the displacement of this object, as it travels from W to X is:
•
W
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• Z
.....
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...
Y ••••••••.••••.•••••••
•
X •
A. ←
B. ↓
C. ↑
D.
E.
ans: E
27. A toy racing car moves with constant speed around the circle shown below. When it is at point
A its coordinates are x = 0, y = 3 m and its velocity is (6 m/s) î. When it is at point B its
velocity and acceleration are:
y
•A
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B•
A.
B.
C.
D.
E.
x
2
−(6 m/s) ĵ and (12 m/s ) î, respectively
2
(6 m/s) î and −(12 m/s ) î, respectively
2
(6 m/s) ĵ and (12 m/s ) î, respectively
2
(6 m/s) î and (2 m/s ) ĵ, respectively
(6 m/s) ĵ and 0, respectively
ans: C
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
43 28. An airplane makes a gradual 90◦ turn while flying at a constant speed of 200 m/s. The process
takes 20.0 seconds to complete. For this turn the magnitude of the average acceleration of the
plane is:
A. zero
2
B. 40 m/s
2
C. 20 m/s
2
D. 14 m/s
2
E. 10 m/s
ans: D
29. An airplane is flying north at 500 km/h. It makes a gradual 180◦ turn at constant speed,
changing its direction of travel from north through east to south. The process takes 40 s. The
average acceleration of the plane for this turn (in km/h·s) is:
A. 12.5 km/h · s, north
B. 12.5 km/h · s, east
C. 12.5 km/h · s, south
D. 25 km/h · s, north
E. 25 km/h · s, south
ans: E
30. An object is moving on a circular path of radius π meters at a constant speed of 4.0 m/s. The
time required for one revolution is:
A. 2/π2 s
B. π 2 /2 s
C. π/2 s
D. π 2 /4
E. 2/π s
ans: B
31. A particle moves at constant speed in a circular path. The instantaneous velocity and instantaneous acceleration vectors are:
A. both tangent to the circular path
B. both perpendicular to the circular path
C. perpendicular to each other
D. opposite to each other
E. none of the above
ans: C
32. A stone is tied to a string and whirled at constant speed in a horizontal circle. The speed
is then doubled without changing the length of the string. Afterward the magnitude of the
acceleration of the stone is:
A. the same
B. twice as great
C. four times as great
D. half as great
E. one-fourth as great
ans: C
44
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS 33. Two objects are traveling around different circular orbits with constant speed. They both have
the same acceleration but object A is traveling twice as fast as object B. The orbit radius for
object A is
the orbit radius for object B.
A. one-fourth
B. one-half
C. the same as
D. twice
E. four times
ans: E
34. A stone is tied to a 0.50-m string and whirled at a constant speed of 4.0 m/s in a vertical circle.
Its acceleration at the top of the circle is:
2
A. 9.8 m/s , up
B. 9.8 m/s2 , down
2
C. 8.0 m/s , down
2
D. 32 m/s , up
2
E. 32 m/s , down
ans: E
35. A stone is tied to a 0.50-m string and whirled at a constant speed of 4.0 m/s in a vertical circle.
Its acceleration at the bottom of the circle is:
2
A. 9.8 m/s , up
B. 9.8 m/s2 , down
C. 8.0 m/s2 , up
2
D. 32 m/s , up
2
E. 32 m/s , down
ans: D
36. A car rounds a 20-m radius curve at 10 m/s. The magnitude of its acceleration is:
A. 0
2
B. 0.20 m/s
2
C. 5.0 m/s
D. 40 m/s2
2
E. 400 m/s
ans: C
37. For a biological sample in a 1.0-m radius centrifuge to have a centripetal acceleration of 25g
its speed must be:
A. 11 m/s
B. 16 m/s
C. 50 m/s
D. 122 m/s
E. 245 m/s
ans: B
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
45 38. A girl jogs around a horizontal circle with a constant speed. She travels one fourth of a
revolution, a distance of 25 m along the circumference of the circle, in 5.0 s. The magnitude of
her acceleration is:
2
A. 0.31 m/s
B. 1.3 m/s2
C. 1.6 m/s2
2
D. 3.9 m/s
2
E. 6.3 m/s
ans: C
39. A stone is tied to the end of a string and is swung with constant speed around a horizontal
circle with a radius of 1.5 m. If it makes two complete revolutions each second, the magnitude
of its acceleration is:
2
A. 0.24 m/s
2
B. 2.4 m/s
C. 24 m/s2
2
D. 240 m/s
2
E. 2400 m/s
ans: D
40. A Ferris wheel with a radius of 8.0 m makes 1 revolution every 10 s. When a passenger is at
the top, essentially a diameter above the ground, he releases a ball. How far from the point on
the ground directly under the release point does the ball land?
A. 0
B. 1.0 m
C. 8.0 m
D. 9.1 m
E. 16 m
ans: D
41. A boat is able to move through still water at 20 m/s. It makes a round trip to a town 3.0 km
upstream. If the river flows at 5 m/s, the time required for this round trip is:
A. 120 s
B. 150 s
C. 200 s
D. 300 s
E. 320 s
ans: E
46
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS 42. A boat is traveling upstream at 14 km/h with respect to a river that is flowing at 6 km/h (with
respect to the ground). A man runs directly across the boat, from one side to the other, at
6 km/h (with respect to the boat). The speed of the man with respect to the ground is:
A. 10 km/h
B. 14 km/h
C. 18.5 km/h
D. 21 km/h
E. 26 km/h
ans: A
43. A ferry boat is sailing at 12 km/h 30◦ W of N with respect to a river that is flowing at 6.0 km/h
E. As observed from the shore, the ferry boat is sailing:
A. 30◦ E of N
B. due N
C. 30◦ W of N
D. 45◦ E of N
E. none of these
ans: B
44. A boy wishes to row across a river in the shortest possible time. He can row at 2 m/s in still
water and the river is flowing at 1 m/s. At what angle θ should he point the bow (front) of his
boat?
....
..
..
∼∼∼∼ .... .....
∼∼∼∼
..
∼∼∼∼ ... .....
θ
A.
B.
C.
D.
E.
...
... ...
... .
...
.................
...
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...
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.
...
...
......
...
....
....
.... .......
....
..... .
...
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...
..
..............................................
.....
1 m/s
∼∼∼∼
∼∼∼∼
30◦
45◦
60◦
63◦
90◦
ans: E
Chapter 4:
MOTION IN TWO AND THREE DIMENSIONS
47 45. A girl wishes to swim across a river to a point directly opposite as shown. She can swim at
2 m/s in still water and the river is flowing at 1 m/s. At what angle θ with respect to the line
joining the starting and finishing points should she swim?
finish
•
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•
start
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....
.....
. ....
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