Halliday/Resnick/Walker Fundamentals of Physics

1
Halliday/Resnick/WalkerFundamentals of Physics

• Classroom Response System Questions

Chapter 6 Forces and Motion II
Interactive Lecture Questions
2
6.3.1. Jennifer is pushing a heavy box up a rough
inclined surface at a constant speed by applying
a horizontal force as shown in the drawing.
The coefficient of kinetic friction for the box
on the inclined surface is ?k. Which one of the
following expressions correctly determines the
normal force on the box? a) b) c) d) e)
3
6.3.1. Jennifer is pushing a heavy box up a rough
inclined surface at a constant speed by applying
a horizontal force as shown in the drawing.
The coefficient of kinetic friction for the box
on the inclined surface is ?k. Which one of the
following expressions correctly determines the
normal force on the box? a) b) c) d) e)
4
6.3.2. Three pine blocks, each with identical
mass, are sitting on a rough surface as shown.
If the same horizontal force is applied to each
block, which one of the following statements is
false? a) The coefficient of kinetic
friction is the same for all three blocks. b)
The magnitude of the force of kinetic friction is
greater for block 3. c) The normal force
exerted by the surface is the same for all three
blocks. d) Block 3 has the greatest apparent
area in contact with the surface. e) If the
horizontal force is the minimum to start block 1
moving, then that same force could be used to
start block 2 or block 3 moving.
5
6.3.2. Three pine blocks, each with identical
mass, are sitting on a rough surface as shown.
If the same horizontal force is applied to each
block, which one of the following statements is
false? a) The coefficient of kinetic
friction is the same for all three blocks. b)
The magnitude of the force of kinetic friction is
greater for block 3. c) The normal force
exerted by the surface is the same for all three
blocks. d) Block 3 has the greatest apparent
area in contact with the surface. e) If the
horizontal force is the minimum to start block 1
moving, then that same force could be used to
start block 2 or block 3 moving.
6
6.3.3. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
that there is no slipping of the top crate as a
horizontal force is applied to the bottom
crate, determine an expression for the magnitude
of the static frictional force acting on the top
crate. a) b) c) d) e)
7
6.3.3. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
that there is no slipping of the top crate as a
horizontal force is applied to the bottom
crate, determine an expression for the magnitude
of the static frictional force acting on the top
crate. a) b) c) d) e)
8
6.3.4. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
a horizontal force is applied to the bottom
crate, determine an expression for the minimum
static coefficient of friction so that the top
crate does not slip. a) b) c) d) e)
9
6.3.4. A crate of mass m is at rest on a
horizontal frictionless surface. Another
identical crate is placed on top of it. Assuming
a horizontal force is applied to the bottom
crate, determine an expression for the minimum
static coefficient of friction so that the top
crate does not slip. a) b) c) d) e)
10
6.3.5. On a rainy evening, a truck is driving
along a straight, level road at 25 m/s. The
driver panics when a deer runs onto the road and
locks the wheels while braking. If the
coefficient of friction for the wheel/road
interface is 0.68, how far does the truck slide
before it stops? a) 55 m b) 47 m c) 41
m d) 36 m e) 32 m
11
6.3.5. On a rainy evening, a truck is driving
along a straight, level road at 25 m/s. The
driver panics when a deer runs onto the road and
locks the wheels while braking. If the
coefficient of friction for the wheel/road
interface is 0.68, how far does the truck slide
before it stops? a) 55 m b) 47 m c) 41
m d) 36 m e) 32 m
12
6.3.6. Jake bought a new dog and is carrying a
new dog house on the flatbed of his brand new
pickup truck. Jake isnt sure if he should tie
the house down, but he doesnt want it to scratch
the paint if it should slide during braking.
During the trip home, Jake will travel along
straight, level roads and have to stop from a
maximum speed of 21 m/s in a distance of 29 m.
What is the minimum coefficient of static
friction between the dog house and the flatbed
that is required to prevent it from sliding?
Compare your answer to the actual coefficient of
static friction of 0.35 to determine if the dog
house should be tied down. a) 0.22, no need to
tie the house down b) 0.30, no need to tie the
house down c) 0.35, he may want to tie it
downjust in case d) 0.56, the house needs to
be tied down e) 0.78, the house needs to be
tied down
13
6.3.6. Jake bought a new dog and is carrying a
new dog house on the flatbed of his brand new
pickup truck. Jake isnt sure if he should tie
the house down, but he doesnt want it to scratch
the paint if it should slide during braking.
During the trip home, Jake will travel along
straight, level roads and have to stop from a
maximum speed of 21 m/s in a distance of 29 m.
What is the minimum coefficient of static
friction between the dog house and the flatbed
that is required to prevent it from sliding?
Compare your answer to the actual coefficient of
static friction of 0.35 to determine if the dog
house should be tied down. a) 0.22, no need to
tie the house down b) 0.30, no need to tie the
house down c) 0.35, he may want to tie it
downjust in case d) 0.56, the house needs to
be tied down e) 0.78, the house needs to be
tied down
14
6.3.7. A block of mass m is pressed against a
wall with an initial force and the block is at
rest. The coefficient of static friction for the
block against the wall is equal to 0.5. The
coefficient of kinetic friction is less than the
coefficient of static friction. If the force is
equal to the weight of the block, which one of
the following statements is true? a) The block
will continue to remain at rest because the force
of static friction is two times the weight of
the block. b) The block will slide down the
wall because the force of static friction is only
equal to one-half of the blocks weight. c) The
block will accelerate at 9.8 m/s2 down the
wall. d) The block will slide down the wall at
constant speed. e) The block will accelerate at
less than 4.9 m/s2 down the wall.
15
6.3.7. A block of mass m is pressed against a
wall with an initial force and the block is at
rest. The coefficient of static friction for the
block against the wall is equal to 0.5. The
coefficient of kinetic friction is less than the
coefficient of static friction. If the force is
equal to the weight of the block, which one of
the following statements is true? a) The block
will continue to remain at rest because the force
of static friction is two times the weight of
the block. b) The block will slide down the
wall because the force of static friction is only
equal to one-half of the blocks weight. c) The
block will accelerate at 9.8 m/s2 down the
wall. d) The block will slide down the wall at
constant speed. e) The block will accelerate at
less than 4.9 m/s2 down the wall.
16
6.3.8. A 1.0 kg block is placed against a wall
and is held stationary by a force of 8.0 N
applied at a 45 angle as shown in the drawing.
What is the magnitude of the friction force? a)
3.7 N b) 4.1 N c) 5.8 N d) 7.0 N e) 8.0 N
17
6.3.8. A 1.0 kg block is placed against a wall
and is held stationary by a force of 8.0 N
applied at a 45 angle as shown in the drawing.
What is the magnitude of the friction force? a)
3.7 N b) 4.1 N c) 5.8 N d) 7.0 N e) 8.0 N
18
6.3.9. A rancher puts a hay bail into the back of
her SUV. Later, she drives around an unbanked
curve with a radius of 48 m at a speed of 16 m/s.
What is the minimum coefficient of static
friction for the hay bail on the floor of the SUV
so that the hay bail does not slide while on the
curve? a) This cannot be determined without
knowing the mass of the hay bail. b) 0.17 c)
0.33 d) 0.42 e) 0.54
19
6.3.9. A rancher puts a hay bail into the back of
her SUV. Later, she drives around an unbanked
curve with a radius of 48 m at a speed of 16 m/s.
What is the minimum coefficient of static
friction for the hay bail on the floor of the SUV
so that the hay bail does not slide while on the
curve? a) This cannot be determined without
knowing the mass of the hay bail. b) 0.17 c)
0.33 d) 0.42 e) 0.54
20
6.4.1. Consider the following situations (i) A
minivan is following a hairpin turn on a mountain
road at a constant speed of twenty miles per
hour. (ii) A parachutist is descending at a
constant speed 10 m/s. (iii) A heavy crate has
been given a quick shove and is now sliding
across the floor. (iv) Jenny is swinging back and
forth on a swing at the park. (v) A football that
was kicked is flying through the goal posts. (vi)
A plucked guitar string vibrates at a constant
frequency. In which one of these situations does
the object or person experience zero
acceleration? a) i only b) ii only c) iii
and iv only d) iv, v, and vi only e) all of
the situations
21
6.4.1. Consider the following situations (i) A
minivan is following a hairpin turn on a mountain
road at a constant speed of twenty miles per
hour. (ii) A parachutist is descending at a
constant speed 10 m/s. (iii) A heavy crate has
been given a quick shove and is now sliding
across the floor. (iv) Jenny is swinging back and
forth on a swing at the park. (v) A football that
was kicked is flying through the goal posts. (vi)
A plucked guitar string vibrates at a constant
frequency. In which one of these situations does
the object or person experience zero
acceleration? a) i only b) ii only c) iii
and iv only d) iv, v, and vi only e) all of
the situations
22
6.4.2. A sky diver jumps from a flying airplane
and falls for several seconds before she reaches
terminal velocity. She then opens her parachute,
reaches a new terminal velocity, and continues
her descent to the ground. Which one of the
following graphs of the drag force versus time
best represents this situation?
23
6.4.2. A sky diver jumps from a flying airplane
and falls for several seconds before she reaches
terminal velocity. She then opens her parachute,
reaches a new terminal velocity, and continues
her descent to the ground. Which one of the
following graphs of the drag force versus time
best represents this situation?
24
6.4.3. A feather and a minivan are dropped
vertically downward from a height of twenty
meters and both are subject to air drag as they
fall. The minivan reaches the ground much faster
than the feather. Which one of the following
statements concerning this situation is true, if
any? a) The minivan has a larger terminal
velocity than the feather because it experiences
less air resistance than the feather. b) The
minivan encounters a smaller force of air
resistance than the feather and falls faster. c)
Each object experiences the same amount of air
drag, but the minivan experiences the greatest
force of gravity. d) The feather experiences
more air drag than the minivan and has a smaller
terminal velocity. e) None of the above
statements are true.
25
6.4.3. A feather and a minivan are dropped
vertically downward from a height of twenty
meters and both are subject to air drag as they
fall. The minivan reaches the ground much faster
than the feather. Which one of the following
statements concerning this situation is true, if
any? a) The minivan has a larger terminal
velocity than the feather because it experiences
less air resistance than the feather. b) The
minivan encounters a smaller force of air
resistance than the feather and falls faster. c)
Each object experiences the same amount of air
drag, but the minivan experiences the greatest
force of gravity. d) The feather experiences
more air drag than the minivan and has a smaller
terminal velocity. e) None of the above
statements are true.
26
6.4.4. A light ping-pong ball and a heavy rubber
ball of exactly the same size are each launched
at the same angle and initial velocity, but the
rubber ball goes much farther than the ping-pong
ball. Which one of the following statements best
explains this result? a) The ping-pong ball
weighs less, so the acceleration due to gravity
is smaller for it. b) The drag force on the
ping-pong ball is larger. c) The ping-pong ball
has less momentum. d) The ping-pong ball has
less mass, so the same drag force slows the
ping-pong ball down more. e) The ping-pong ball
has a smaller moment of inertia since it is
hollow and weighs less.
27
6.4.4. A light ping-pong ball and a heavy rubber
ball of exactly the same size are each launched
at the same angle and initial velocity, but the
rubber ball goes much farther than the ping-pong
ball. Which one of the following statements best
explains this result? a) The ping-pong ball
weighs less, so the acceleration due to gravity
is smaller for it. b) The drag force on the
ping-pong ball is larger. c) The ping-pong ball
has less momentum. d) The ping-pong ball has
less mass, so the same drag force slows the
ping-pong ball down more. e) The ping-pong ball
has a smaller moment of inertia since it is
hollow and weighs less.
28
6.5.1. A ball is whirled on the end of a string
in a horizontal circle of radius R at constant
speed v. By which one of the following means can
the centripetal acceleration of the ball be
increased by a factor of two? a) Keep the
radius fixed and increase the period by a factor
of two. b) Keep the radius fixed and decrease
the period by a factor of two. c) Keep the
speed fixed and increase the radius by a factor
of two. d) Keep the speed fixed and decrease
the radius by a factor of two. e) Keep the
radius fixed and increase the speed by a factor
of two.
29
6.5.1. A ball is whirled on the end of a string
in a horizontal circle of radius R at constant
speed v. By which one of the following means can
the centripetal acceleration of the ball be
increased by a factor of two? a) Keep the
radius fixed and increase the period by a factor
of two. b) Keep the radius fixed and decrease
the period by a factor of two. c) Keep the
speed fixed and increase the radius by a factor
of two. d) Keep the speed fixed and decrease
the radius by a factor of two. e) Keep the
radius fixed and increase the speed by a factor
of two.
30
6.5.2. A steel ball is whirled on the end of a
chain in a horizontal circle of radius R with a
constant period T. If the radius of the circle
is then reduced to 0.75R, while the period
remains T, what happens to the centripetal
acceleration of the ball? a) The centripetal
acceleration increases to 1.33 times its initial
value. b) The centripetal acceleration
increases to 1.78 times its initial value. c)
The centripetal acceleration decreases to 0.75
times its initial value. d) The centripetal
acceleration decreases to 0.56 times its initial
value. e) The centripetal acceleration does not
change.
31
6.5.2. A steel ball is whirled on the end of a
chain in a horizontal circle of radius R with a
constant period T. If the radius of the circle
is then reduced to 0.75R, while the period
remains T, what happens to the centripetal
acceleration of the ball? a) The centripetal
acceleration increases to 1.33 times its initial
value. b) The centripetal acceleration
increases to 1.78 times its initial value. c)
The centripetal acceleration decreases to 0.75
times its initial value. d) The centripetal
acceleration decreases to 0.56 times its initial
value. e) The centripetal acceleration does not
change.
32
6.5.3. A boy is whirling a stone at the end of a
string around his head. The string makes one
complete revolution every second, and the tension
in the string is FT. The boy increases the speed
of the stone, keeping the radius of the circle
unchanged, so that the string makes two complete
revolutions per second. What happens to the
tension in the sting? a) The tension increases
to four times its original value. b) The
tension increases to twice its original
value. c) The tension is unchanged. d) The
tension is reduced to one half of its original
value. e) The tension is reduced to one fourth
of its original value.
33
6.5.3. A boy is whirling a stone at the end of a
string around his head. The string makes one
complete revolution every second, and the tension
in the string is FT. The boy increases the speed
of the stone, keeping the radius of the circle
unchanged, so that the string makes two complete
revolutions per second. What happens to the
tension in the sting? a) The tension increases
to four times its original value. b) The
tension increases to twice its original
value. c) The tension is unchanged. d) The
tension is reduced to one half of its original
value. e) The tension is reduced to one fourth
of its original value.
34
6.5.4. An aluminum rod is designed to break when
it is under a tension of 600 N. One end of the
rod is connected to a motor and a 12-kg spherical
object is attached to the other end. When the
motor is turned on, the object moves in a
horizontal circle with a radius of 6.0 m. If the
speed of the motor is continuously increased, at
what speed will the rod break? Ignore the mass
of the rod for this calculation. a) 11 m/s b)
17 m/s c) 34 m/s d) 88 m/s e) 3.0 102 m/s
35
6.5.4. An aluminum rod is designed to break when
it is under a tension of 600 N. One end of the
rod is connected to a motor and a 12-kg spherical
object is attached to the other end. When the
motor is turned on, the object moves in a
horizontal circle with a radius of 6.0 m. If the
speed of the motor is continuously increased, at
what speed will the rod break? Ignore the mass
of the rod for this calculation. a) 11 m/s b)
17 m/s c) 34 m/s d) 88 m/s e) 3.0 102 m/s
36
6.5.5. A ball is attached to a string and whirled
in a horizontal circle. The ball is moving in
uniform circular motion when the string separates
from the ball (the knot wasnt very tight).
Which one of the following statements best
describes the subsequent motion of the ball? a)
The ball immediately flies in the direction
radially outward from the center of the circular
path the ball had been following. b) The ball
continues to follow the circular path for a short
time, but then it gradually falls away. c) The
ball gradually curves away from the circular path
it had been following. d) The ball immediately
follows a linear path away from, but not tangent
to the circular path it had been following. e)
The ball immediately follows a line that is
tangent to the circular path the ball had been
following
37
6.5.5. A ball is attached to a string and whirled
in a horizontal circle. The ball is moving in
uniform circular motion when the string separates
from the ball (the knot wasnt very tight).
Which one of the following statements best
describes the subsequent motion of the ball? a)
The ball immediately flies in the direction
radially outward from the center of the circular
path the ball had been following. b) The ball
continues to follow the circular path for a short
time, but then it gradually falls away. c) The
ball gradually curves away from the circular path
it had been following. d) The ball immediately
follows a linear path away from, but not tangent
to the circular path it had been following. e)
The ball immediately follows a line that is
tangent to the circular path the ball had been
following
38
6.5.6. Complete the following statement The
maximum speed at which a car can safely negotiate
an unbanked curve depends on all of the following
factors except a) the coefficient of kinetic
friction between the road and the tires. b) the
coefficient of static friction between the road
and the tires. c) the acceleration due to
gravity. d) the diameter of the curve. e) the
ratio of the static frictional force between the
road and the tires and the normal force exerted
on the car.
39
6.5.6. Complete the following statement The
maximum speed at which a car can safely negotiate
an unbanked curve depends on all of the following
factors except a) the coefficient of kinetic
friction between the road and the tires. b) the
coefficient of static friction between the road
and the tires. c) the acceleration due to
gravity. d) the diameter of the curve. e) the
ratio of the static frictional force between the
road and the tires and the normal force exerted
on the car.
40
6.5.7. A 1000-kg car travels along a straight
portion of highway at a constant velocity of 10
m/s, due east. The car then encounters an
unbanked curve of radius 50 m. The car follows
the curve traveling at a constant speed of 10 m/s
while the direction of the car changes from east
to south. What is the magnitude of the
frictional force between the tires and the road
as the car negotiates the unbanked curve? a)
500 N b) 1000 N c) 2000 N d) 5000 N e) 10
000 N
41
6.5.7. A 1000-kg car travels along a straight
portion of highway at a constant velocity of 10
m/s, due east. The car then encounters an
unbanked curve of radius 50 m. The car follows
the curve traveling at a constant speed of 10 m/s
while the direction of the car changes from east
to south. What is the magnitude of the
frictional force between the tires and the road
as the car negotiates the unbanked curve? a)
500 N b) 1000 N c) 2000 N d) 5000 N e) 10
000 N
42
6.5.8. A space station is designed in the shape
of a large, hollow donut that is uniformly
rotating. The outer radius of the station is 460
m. With what period must the station rotate so
that a person sitting on the outer wall
experiences artificial gravity, i.e. an
acceleration of 9.8 m/s2? a) 43 s b) 76 s c)
88 s d) 110 s e) 230 s
43
6.5.8. A space station is designed in the shape
of a large, hollow donut that is uniformly
rotating. The outer radius of the station is 460
m. With what period must the station rotate so
that a person sitting on the outer wall
experiences artificial gravity, i.e. an
acceleration of 9.8 m/s2? a) 43 s b) 76 s c)
88 s d) 110 s e) 230 s
44
6.5.9. At a circus, a clown on a motorcycle with
a mass M travels along a horizontal track and
enters a vertical circle of radius r. Which one
of the following expressions determines the
minimum speed that the motorcycle must have at
the top of the track to remain in contact with
the track? a) b) c) v gR d) v 2gR
e) v MgR
45
6.5.9. At a circus, a clown on a motorcycle with
a mass M travels along a horizontal track and
enters a vertical circle of radius r. Which one
of the following expressions determines the
minimum speed that the motorcycle must have at
the top of the track to remain in contact with
the track? a) b) c) v gR d) v 2gR
e) v MgR
46
6.5.10. A ball on the end of a rope is moving in
a vertical circle near the surface of the earth.
Point A is at the top of the circle C is at the
bottom. Points B and D are exactly halfway
between A and C. Which one of the following
statements concerning the tension in the rope is
true? a) The tension is smallest at point
A. b) The tension is smallest at point C. c)
The tension is smallest at both points B and
D. d) The tension is the same at points A and
C. e) The tension is the same at all four
points.
47
6.5.10. A ball on the end of a rope is moving in
a vertical circle near the surface of the earth.
Point A is at the top of the circle C is at the
bottom. Points B and D are exactly halfway
between A and C. Which one of the following
statements concerning the tension in the rope is
true? a) The tension is smallest at point
A. b) The tension is smallest at point C. c)
The tension is smallest at both points B and
D. d) The tension is the same at points A and
C. e) The tension is the same at all four
points.
48
6.5.11. Imagine you are swinging a bucket by the
handle around in a circle that is nearly level
with the ground (a horizontal circle). What is
the force, the physical force, holding the bucket
in a circular path? a) the centripetal
force b) the centrifugal force c) your hand
on the handle d) gravitational force e) None
of the above are correct.
49
6.5.11. Imagine you are swinging a bucket by the
handle around in a circle that is nearly level
with the ground (a horizontal circle). What is
the force, the physical force, holding the bucket
in a circular path? a) the centripetal
force b) the centrifugal force c) your hand
on the handle d) gravitational force e) None
of the above are correct.
50
6.5.12. Imagine you are swinging a bucket by the
handle around in a circle that is nearly level
with the ground (a horizontal circle). Now
imagine there's a ball in the bucket. What keeps
the ball moving in a circular path? a) contact
force of the bucket on the ball b) contact
force of the ball on the bucket c)
gravitational force on the ball d) the
centripetal force e) the centrifugal force
51
6.5.12. Imagine you are swinging a bucket by the
handle around in a circle that is nearly level
with the ground (a horizontal circle). Now
imagine there's a ball in the bucket. What keeps
the ball moving in a circular path? a) contact
force of the bucket on the ball b) contact
force of the ball on the bucket c)
gravitational force on the ball d) the
centripetal force e) the centrifugal force
52
6.5.13. Which of the following parameters
determine how fast you need to swing a water
bucket vertically so that water in the bucket
will not fall out? a) radius of swing b) mass
of bucket c) mass of water d) a and b e) a
and c
53
6.5.13. Which of the following parameters
determine how fast you need to swing a water
bucket vertically so that water in the bucket
will not fall out? a) radius of swing b) mass
of bucket c) mass of water d) a and b e) a
and c
54
6.5.14. The moon, which is approximately 4 109
m from Earth, has a mass of 7.4 1022 kg and a
period of 27.3 days. What must is the magnitude
of the gravitational force between the Earth and
the moon? a) 1.8 1018 N b) 2.1 1022 N c)
1.7 1013 N d) 5.0 1022 N e) 4.2 1020 N
55
6.5.14. The moon, which is approximately 4 109
m from Earth, has a mass of 7.4 1022 kg and a
period of 27.3 days. What must is the magnitude
of the gravitational force between the Earth and
the moon? a) 1.8 1018 N b) 2.1 1022 N c)
1.7 1013 N d) 5.0 1022 N e) 4.2 1020 N
56
6.5.15. The Rapid Rotor is spinning fast enough
that the floor beneath the rider drops away and
the rider remains in place. If the Rotor speeds
up until it is going twice as fast as it was
previously, what is the effect on the frictional
force on the rider? a) The frictional force is
reduced to one-fourth of its previous value. b)
The frictional force is the same as its previous
value. c) The frictional force is reduced to
one-half of its previous value. d) The
frictional force is increased to twice its
previous value. e) The frictional force is
increased to four times its previous value.
57
6.5.15. The Rapid Rotor is spinning fast enough
that the floor beneath the rider drops away and
the rider remains in place. If the Rotor speeds
up until it is going twice as fast as it was
previously, what is the effect on the frictional
force on the rider? a) The frictional force is
reduced to one-fourth of its previous value. b)
The frictional force is the same as its previous
value. c) The frictional force is reduced to
one-half of its previous value. d) The
frictional force is increased to twice its
previous value. e) The frictional force is
increased to four times its previous value.