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Halliday/Resnick/Walker Fundamentals of Physics

- Classroom Response System Questions

Chapter 6 Forces and Motion II

Interactive Lecture Questions

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)

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)

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.

6.3.2. 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.

6.3.3. 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)

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)

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)

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)

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

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

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

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

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.

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.

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

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

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

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

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

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

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?

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?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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

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

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.

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.

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

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

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

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

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

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

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.

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.

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.

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.

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

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

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

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

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

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

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.

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.