PHYSICS Principles and Problems

Chapter 4 Forces in One Dimension

Forces in One Dimension

CHAPTER4

BIG IDEA

- Net forces cause changes in motion.

Table Of Contents

CHAPTER4

Section 4.1 Force and Motion Section 4.2

Weight and Drag Force Section 4.3 Newtons

Third Law

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slides.

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Force and Motion

SECTION4.1

MAIN IDEA A force is a push or a pull.

Essential Questions

- What is a force?
- What is the relationship between force and

acceleration? - How does motion change when the net force is

zero?

Force and Motion

SECTION4.1

- Review Vocabulary
- Acceleration the rate at which the velocity of an

object changes.

- New Vocabulary
- Force
- System
- Free-body diagram
- Newtons second law

- Newtons first law
- Inertia
- Equilibrium

Force and Motion

SECTION4.1

Force

- Consider a textbook resting on a table. To cause

it to move, you could either push or pull on it. - A force is defined as a push or pull exerted on

an object.

Force and Motion

SECTION4.1

Force (cont.)

- If you push harder on an object, you have a

greater effect on its motion. - The direction in which force is exerted also

matters. If you push the book to the right, the

book moves to the right. - The symbol F is a vector and represents the size

and direction of a force, while F represents only

the magnitude.

Force and Motion

SECTION4.1

Force (cont.)

- Forces can cause objects to speed up, slow down,

or change direction as they move. - Based on the definitions of velocity and

acceleration, a force exerted on an object causes

that objects velocity to change that is, a

force causes an acceleration. - All accelerations are the result of an unbalanced

force acting on an object.

Force and Motion

SECTION4.1

Force (cont.)

- When considering how a force affects motion, it

is important to identify the object of interest.

This object is called the system. - Everything around the object that exerts forces

on it is called the external world.

Force and Motion

SECTION4.1

Force (cont.)

- Think about the different ways in which you could

move a textbook. - You could touch it directly and push or pull it,

or you could tie a string around it and pull on

the string. These are examples of contact forces.

Force and Motion

SECTION4.1

Force (cont.)

- A contact force exists when an object from the

external world touches a system and thereby

exerts a force on it.

Force and Motion

SECTION4.1

Force (cont.)

- There are other ways in which the motion of the

textbook can change. - If you drop a book, the gravitational force of

Earth causes the book to accelerate, whether or

not Earth is actually touching it. This is an

example of a field force. - Field forces are exerted without contact.

Force and Motion

SECTION4.1

Force (cont.)

- Forces result from interactions thus, each force

has a specific and identifiable cause called the

agent. - Without both an agent and a system, a force does

not exist. - A physical model which represents the forces

acting on a system, is called a free-body diagram.

Force and Motion

SECTION4.1

Force (cont.)

Click image to view movie.

Force and Motion

SECTION4.1

Combining Forces

- When the force vectors are in the same direction,

they can be replaced by a vector with a length

equal to their combined length. - If the forces are in opposite directions, the

resulting vector is the length of the difference

between the two vectors, in the direction of the

greater force. - Vector sum of all the forces on an object is net

force.

Force and Motion

SECTION4.1

Acceleration and Force

- To explore how forces affect an objects motion,

consider the situation explored in the figure, in

which, a horizontal force is exerted on an

object.

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

- Notice, in order to reduce complications

resulting from the object rubbing against the

surface, the investigation was performed on a

smooth, well-polished table and the cart has

wheels.

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

- To exert a constant force, a spring scale was

used to pull the cart. - The velocity of the cart was measured for a

period of time. - Using the data, a velocity-time graph was

constructed.

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

- The data indicates for a constant force there is

a constant acceleration on an object. - Thus, indicating the relationship between force

and acceleration is linear and allowing the

application of the equation for a straight line - The y-intercept is 0, so the linear equation

simplifies to ykx. The y-variable is

acceleration and x-variable is force.

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

- What is the physical meaning of the slope of the

acceleration-force graph? - To determine this, increase the number of carts

gradually.

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

- A plot of the force versus acceleration for one,

two, and three carts indicates that if the same

force is applied in each situation, the

acceleration of two carts is the acceleration

of one cart and the acceleration of three carts

is the acceleration of one cart.

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

- This means that as the number of carts is

increased, a greater force is needed to produce

the same acceleration. - The slopes of the lines in the graph depend upon

the number of carts that is, the slope depends

on the total mass of the carts.

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

Force and Motion

SECTION4.1

Acceleration and Force (cont.)

- The formula, F ma, tells you that if you double

the force, you will double the objects

acceleration. - If you apply the same force to several different

objects, the one with the most mass will have the

smallest acceleration and the one with the least

mass will have the greatest acceleration. - One unit of force causes a 1-kg mass to

accelerate at 1 m/s2, so one force unit has the

dimensions 1 kgm/s2 or one newton and is

represented by N.

Force and Motion

SECTION4.1

Newtons Second Law

- The observation that acceleration of an object is

proportional to the net force exerted on it and

inversely proportional to its mass is Newtons

second law, which can be represented in the

following equation.

- Newtons second law states that the acceleration

of an object is equal to the sum of the forces

(the net force) acting on the object, divided by

the mass of the object.

Force and Motion

SECTION4.1

Newtons Second Law (cont.)

- One of the most important steps in correctly

applying Newtons second law is determining the

net force acting on the object. - Draw a free-body diagram showing the direction

and relative strength of each force acting on the

system. - Then add the force vectors to find the net force.

Force and Motion

SECTION4.1

Newtons Second Law (cont.)

- Next, use Newtons second law to calculate the

acceleration. - Finally, if necessary, use what you know about

accelerated motion to find the velocity or

position of the object.

Force and Motion

SECTION4.1

Fighting Over a Toy

Anudja is holding a stuffed dog with a mass of

0.30 kg, when Sarah decides that she wants it and

tries to pull it away from Anudja. If Sarah pulls

horizontally on the dog with a force of 10.0 N

and Anudja pulls with a horizontal force of 11.0

N, what is the horizontal acceleration of the dog?

Force and Motion

SECTION4.1

Fighting Over a Toy

Step 1 Analyze and Sketch the Problem

- Sketch the situation.
- Identify the stuffed dog as the system and the

direction in which Anudja pulls as positive. - Draw the free-body diagram. Label the force.

Force and Motion

SECTION4.1

Fighting Over a Toy

Step 2 Solve for the Unknown

Force and Motion

SECTION4.1

Fighting Over a Toy

Identify known and unknown variables.

Known m 0.30 kg FAnudja on dog 11.0 N

FSarah on dog 10.0 N

Unknown a ?

Force and Motion

SECTION4.1

Fighting Over a Toy

Use Newtons second law to solve for a.

Fnet FAnudja on dog (-FSarah on dog)

Force and Motion

SECTION4.1

Fighting Over a Toy

Substitute Fnet FAnudja on dog (FSarah on

dog)

Force and Motion

SECTION4.1

Fighting Over a Toy

Substitute FAnudja on dog 11.0 N, FSarah on dog

10.0 N, m 0.30 kg

Force and Motion

SECTION4.1

Fighting Over a Toy

Step 3 Evaluate the Answer

Force and Motion

SECTION4.1

Fighting Over a Toy

- Are the units correct?
- m/s2 is the correct unit for acceleration.
- Does the sign make sense?
- The acceleration is in the positive direction

because Anudja is pulling in the positive

direction with a greater force than Sarah is

pulling in the negative direction.

Force and Motion

SECTION4.1

Fighting Over a Toy

- Is the magnitude realistic?
- It is a reasonable acceleration for a light,

stuffed toy.

Force and Motion

SECTION4.1

Fighting Over a Toy

The steps covered were

- Step 1 Analyze and Sketch the Problem
- Sketch the situation.
- Identify the stuffed dog as the system and the

direction in which Anudja pulls as positive. - Draw the free-body diagram. Label the forces.

Force and Motion

SECTION4.1

Fighting Over a Toy

The steps covered were

- Step 2 Solve for the Unknown
- Step 3 Evaluate the Answer

Force and Motion

SECTION4.1

Newtons First Law

- What is the motion of an object with no net force

acting on it? - Newtons second law states says that if net force

is zero, then acceleration equal zero. - If acceleration is zero, then velocity does not

change. - A stationary object with no net force acting on

it will stay at rest.

Force and Motion

SECTION4.1

Newtons First Law (cont.)

- What about a moving object like a rolling ball?

How long will it roll? - Depends on the surface thick carpet exerts more

force than a smooth hard surface like a bowling

alley. - So the ball will stop rolling sooner on the

carpet than the bowling alley.

Force and Motion

SECTION4.1

Newtons First Law (cont.)

- Galileo did many experiments, and he concluded

that in the ideal case of zero resistance,

horizontal motion would never stop. - Galileo was the first to recognize that the

general principles of motion could be found by

extrapolating experimental results to the ideal

case, in which there is no resistance to slow

down an objects motion.

Force and Motion

SECTION4.1

Newtons First Law (cont.)

- In the absence of a net force, the motion (or

lack of motion) of both the moving object and the

stationary object continues as it was. Newton

recognized this and generalized Galileos results

in a single statement. - This statement, an object that is at rest will

remain at rest, and an object that is moving will

continue to move in a straight line with constant

speed, if and only if the net force acting on

that object is zero, is called Newtons first

law.

Force and Motion

SECTION4.1

Newtons First Law (cont.)

- Newtons first law is sometimes called the law of

inertia. - Inertia is the tendency of an object to resist

change. - If an object is at rest, it tends to remain at

rest. - If it is moving at a constant velocity, it tends

to continue moving at that velocity. - Forces are results of interactions between two

objects they are not properties of single

objects, so inertia cannot be a force.

Force and Motion

SECTION4.1

Newtons First Law (cont.)

- If the net force on an object is zero, then the

object is in equilibrium. - An object is in equilibrium if its velocity is

not changing. - Newtons first law identifies a net force as

something that disturbs the state of equilibrium. - Thus, if there is no net force acting on the

object, then the object does not experience a

change in speed or direction and is in

equilibrium.

Force and Motion

SECTION4.1

Newtons First Law (cont.)

- Some of the common types of forces are displayed

on the right. - When analyzing forces and motion, it is important

to keep in mind that the world is dominated by

resistance. Newtons ideal, resistance-free world

is not easy to visualize.

Section Check

SECTION4.1

- Two horses are pulling a 100-kg cart in the same

direction, applying a force of 50 N each. What is

the acceleration of the cart?

A. 2 m/s2 B. 1 m/s2 C. 0.5 m/s2 D. 0 m/s2

Section Check

SECTION4.1

Answer

Section Check

SECTION4.1

- Two friends Mary and Maria are trying to pull a

10-kg chair in opposite directions. If Maria

applied a force of 60 N and Mary applied a force

of 40 N, in which direction will the chair move

and with what acceleration?

Section Check

SECTION4.1

A. The chair will move towards Mary with an

acceleration of 2 m/s2. B. The chair will move

towards Mary with an acceleration of 10 m/s2. C.

The chair will move towards Maria with an

acceleration of 2 m/s2. D. The chair will move

towards Maria with an acceleration of 10 m/s2.

Section Check

SECTION4.1

Answer

Section Check

SECTION4.1

- State Newtons first law.

Answer Newtons first law states that an object

that is at rest will remain at rest, and an

object that is moving will continue to move in a

straight line with constant speed, if and only if

the net force acting on that object is zero.

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Weight and Drag Force

SECTION4.2

MAIN IDEA Newtons second law can be used to

explain the motion of falling objects.

Essential Questions

- How are the weight and the mass of an object

related? - How do actual weight and apparent weight differ?
- What effect does air have on falling objects?

Weight and Drag Force

SECTION4.2

- Review Vocabulary
- viscosity a fluids resistance to flowing.

- New Vocabulary
- Weight
- Gravitational pull
- Apparent weight

- Weightlessness
- Drag force
- Terminal velocity

Weight and Drag Force

SECTION4.2

Weight

- Weight is the gravitational force experienced by

an object. - This gravitational force is a field force whose

magnitude is directly proportional to the mass of

the object experiencing the force - Fg mg, where m is the mass of the object

and g is the gravitational field. - Because weight is a force, the proper unit used

to measure weight is the newton.

Weight and Drag Force

SECTION4.2

Weight (cont.)

- Gravitational field is a vector quantity that

relates the mass of an object to the

gravitational force it experiences at a given

location. - Near Earths surface, g is 9.8N/kg toward Earths

center.

- When you step on a scale, the scale exerts an

upward force on you equal in magnitude to the

gravitational force pulling down on you.

- The scale is calibrated to convert the stretch of

the springs, the upward force necessary to give a

net force of zero, to weight .

Weight and Drag Force

SECTION4.2

Weight (cont.)

- Apparent weight and weightlessness.

Click image to view movie.

Weight and Drag Force

SECTION4.2

Drag Force

- When an object moves through any fluid, such as

air or water, the fluid exerts a drag force on

the moving object in the direction opposite to

its motion. - A drag force is the force exerted by a fluid on

the object moving through the fluid. - This force is dependent on the motion of the

object, the properties of the object, and the

properties of the fluid (viscosity and

temperature) that the object is moving through.

Weight and Drag Force

SECTION4.2

Drag Force (cont.)

- As a dropped tennis balls velocity increases, so

does the drag force. The constant velocity that

is reached when the drag force equals the force

of gravity is called the terminal velocity.

Weight and Drag Force

SECTION4.2

Drag Force (cont.)

Click image to view movie.

Weight and Drag Force

SECTION4.2

- If the mass of a person on Earth is 20 kg, what

will be his mass on the Moon? (Gravity on the

Moon is six times less than the gravity on Earth.)

Weight and Drag Force

SECTION4.2

Answer

Reason The mass of an object does not change

with the change in gravity, only the weight

changes.

Weight and Drag Force

SECTION4.2

- Your mass is 100 kg, and you are standing on a

bathroom scale in an elevator. What is the scale

reading when the elevator is falling freely?

Weight and Drag Force

SECTION4.2

Answer

Reason Since the elevator is falling freely with

acceleration g, the contact force between the

elevator and you is zero. As scale reading

displays the contact force, it would be zero.

Weight and Drag Force

SECTION4.2

- In which of the following cases will your

apparent weight be greater than your real weight?

A. The elevator is at rest. B. The elevator is

accelerating upward. C. The elevator is

accelerating downward. D. Apparent weight is

never greater than real weight.

Weight and Drag Force

SECTION4.2

Answer

Reason When the elevator is moving upward, your

apparent weight

Fapparent ma Fg (where m is your mass and

a is the acceleration of the elevator). So your

apparent weight becomes more than your real

weight.

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Newtons Third Law

SECTION4.3

MAIN IDEA All forces occur in interaction pairs.

Essential Questions

- What is Newtons third law?
- What is the normal force?

Newtons Third Law

SECTION4.3

- Review Vocabulary
- symmetry correspondence of parts on opposite

sides of a dividing line.

- New Vocabulary
- Interaction pair
- Newtons third law
- Tension
- Normal force

Newtons Third Law

SECTION4.3

Interaction Pairs

- When you exert a force on your friend to push him

forward, he exerts an equal and opposite force on

you, which causes you to move backward.

- The forces FA on B and FB on A are an interaction

pair. - An interaction pair is two forces that are in

opposite directions and have equal magnitude.

Newtons Third Law

SECTION4.3

Interaction Pairs (cont.)

- An interaction pair is also called an

action-reaction pair of forces. - This might suggest that one causes the other

however, this is not true. - For example, the force of you pushing your friend

doesnt cause your friend to exert a force on

you. - The two forces either exist together or not at

all. - They both result from the contact between the two

of you.

Newtons Third Law

SECTION4.3

Interaction Pairs (cont.)

- The force of you on your friend is equal in

magnitude and opposite in direction to the force

of your friend on you. - This is summarized in Newtons third law, which

states that all forces come in pairs.

Newtons Third Law

SECTION4.3

Interaction Pairs (cont.)

- Newtons Third Law states that the force of A on

B is equal in magnitude and opposite in direction

of the force of B on A. - The two forces in a pair act on different objects

and are equal and opposite. - Numerically, FA on B FB on A

Newtons Third Law

SECTION4.3

Interaction Pairs (cont.)

- When identifying an interaction pair, remember

that they always occur in two different free-body

diagrams and they always have the symmetry in

subscripts noted on the previous slide.

Newtons Third Law

SECTION4.3

Earths Acceleration

A softball has a mass of 0.18 kg. What is the

gravitational force on Earth due to the ball, and

what is Earths resulting acceleration? Earths

mass is 6.01024 kg.

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Step 1 Analyze and Sketch the Problem

- Draw free-body diagrams for the two systems the

ball and Earth. - Connect the interaction pair by a dashed line.

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Identify known and unknown variables.

Known mball 0.18 kg mEarth 6.01024 kg g

-9.80 m/s2

Unknown FEarth on ball ? aEarth ?

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Step 2 Solve for the Unknown

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Use Newtons second law to find the weight of the

ball.

FEarth on ball mballg

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Substitute mball 0.18 kg, g -9.80 m/s2

FEarth on ball (0.18 kg)(-9.80 m/s2)

-1.8 N

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Use Newtons third law to solve for Fball on

Earth.

Fball on Earth FEarth on ball

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Substitute FEarth on ball 1.8 N

Fball on Earth ( 1.8 N) 1.8N

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Use Newtons second and third laws to find aEarth.

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Substitute Fnet 1.8 N, mEarth 6.01024 kg

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

Step 3 Evaluate the Answer

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

- Are the units correct?
- Dimensional analysis verifies force in N and

acceleration in m/s2. - Does the sign make sense?
- Force and acceleration should be positive.

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

- Is the magnitude realistic?
- Because of Earths large mass, the acceleration

should be small.

Newtons Third Law

SECTION4.3

Earths Acceleration (cont.)

The steps covered were

- Step 1 Analyze and Sketch the Problem
- Draw free-body diagrams for the two systems the

ball and Earth. - Connect the interaction pair by a dashed line.
- Step 2 Solve for the Unknown
- Step 3 Evaluate the Answer

Newtons Third Law

SECTION4.3

Tension

- The force exerted by a string or rope is called

tension. - At any point in a rope, the tension forces are

pulling equally in both directions.

Newtons Third Law

SECTION4.3

Tension (cont.)

Newtons Third Law

SECTION4.3

The Normal Force

- The normal force is the perpendicular contact

force exerted by a surface on another object. - The normal force is important when calculating

resistance.

Section Check

SECTION4.3

- Explain Newtons third law.

Section Check

SECTION4.3

Answer

- Answer Suppose you push your friend. The force

of you on your friend is equal in magnitude and

opposite in direction to the force of your friend

on you. This is summarized in Newtons third law,

which states that forces come in pairs. The two

forces in a pair act on different objects and are

equal in strength and opposite in direction. - Newtons third law FA on B FB on A
- The force of A on B is equal in magnitude and

opposite in direction of the force of B on A.

Section Check

SECTION4.3

- If a stone is hung from a rope with no mass, at

which place on the rope will there be the most

tension?

A. The top of the rope, near the hook. B. The

bottom of the rope, near the stone. C. The

middle of the rope. D. The tension will be the

same throughout the rope.

Section Check

SECTION4.3

Answer

Reason Because the rope is assumed to be without

mass, the tension everywhere in the rope is equal

to the stones weight.

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Forces in One Dimension

CHAPTER4

Resources

Physics Online Study Guide Chapter Assessment

Questions Standardized Test Practice

Force and Motion

SECTION4.1

Study Guide

- A force is a push or a pull. Forces have both

direction and magnitude. A force might be either

a contact force or a field force. - Newtons second law states that the acceleration

of a system equals the net force acting on it

divided by its mass.

Force and Motion

SECTION4.1

Study Guide

- Newtons first law states that an object that is

at rest will remains at rest and an object that

is moving will continue to move in a straight

line with constant speed, if and only if the net

force acting on that object is zero. An object

with zero net force acting on it is in

equilibrium.

Weight and Drag Force

SECTION4.2

Study Guide

- The objects weight (Fg) depends on the objects

mass and the gravitational field at the objects

location. - An objects apparent weight is the magnitude of

the support force exerted on it. An object with

no apparent weight experiences weightlessness.

Weight and Drag Force

SECTION4.2

Study Guide

- A falling object reaches a constant velocity when

the drag force is equal to the objects weight.

The constant velocity is called the terminal

velocity. The drag force on an object is

determined by the objects weight, size and shape

as well as the fluid through which it moves.

Newtons Third Law

SECTION4.3

Study Guide

- Newtons third law states that the two forces

that make up an interaction pair of forces are

equal in magnitude, but opposite in direction and

act on different objects. In an interaction

pair, FA on B does not cause FB on A. The two

forces either exist together or not at all.

Newtons Third Law

SECTION4.3

Study Guide

- The normal force is a support force resulting

from the contact between two objects. It is

always perpendicular to the plane of contact

between the two objects.

Forces in One Dimension

CHAPTER4

Chapter Assessment

Combining Forces

- If you and your friend exert a force of 100 N

each on a table, first in the same direction and

then in opposite directions, what is the net

force?

Forces in One Dimension

CHAPTER4

Chapter Assessment

Combining Forces

- In the first case, your friend is pushing with a

negative force of 100 N. Adding them together

gives a total force of 0 N.

Forces in One Dimension

CHAPTER4

Chapter Assessment

Combining Forces

- In the second case, your friends force is 100 N,

so the total force is 200 N in the positive

direction and the table accelerates in the

positive direction.

Forces in One Dimension

CHAPTER4

Chapter Assessment

Newtons Second Law

- Newtons second law can be rearranged to the form

F ma, which you

learned about previously. - Assume that the table that you and your friend

were pushing was 15.0 kg and the two of you each

pushed with a force of 50.0 N in the same

direction. - To find out what the acceleration of the table

would be, calculate the net force, 50.0 N 50.0

N 100.0 N, and apply Newtons second law by

dividing the net force of 100.0 N by the mass of

the table, 15.0 kg, to get an acceleration of

6.67 m/s2.

Forces in One Dimension

CHAPTER4

Chapter Assessment

Forces of Ropes and Strings

- Tension forces are at work in a tug-of-war.
- If team A, on the left, is exerting a force of

500 N and the rope does not move, then team B,

must also be pulling with 500 N.

Tim Fuller

Forces in One Dimension

CHAPTER4

Chapter Assessment

Fighting Over a Toy

Anudja is holding a stuffed dog, with a mass of

0.30 kg, when Sarah decides that she wants it and

tries to pull it away from Anudja. If Sarah pulls

horizontally on the dog with a force of 10.0 N

and Anudja pulls with a horizontal force of 11.0

N, what is the horizontal acceleration of the dog?

Forces in One Dimension

CHAPTER4

Chapter Assessment

Earths Acceleration

When a softball with a mass of 0.18 kg is

dropped, its acceleration toward Earth is equal

to g, the acceleration due to gravity. What is

the force on Earth due to the ball, and what is

Earths resulting acceleration? Earths mass is

6.01024 kg.

Forces in One Dimension

CHAPTER4

Chapter Assessment

- If a golf ball, baseball and bowling ball are

thrown with the same force, which ball will move

with a greater acceleration?

A. Golf ball B. Baseball C. Bowling ball D.

The three balls will have equal acceleration.

Forces in One Dimension

CHAPTER4

Chapter Assessment

Forces in One Dimension

CHAPTER4

Chapter Assessment

- Jack is boating in a river applying a contact

force of 30 N, in a direction opposite to the

flow of water. At the same time, the water is

exerting a force of 30 N on the boat. In which

direction will the boat move?

A. The boat will move in the direction of the

flow of water. B. The boat will not move at

all. C. The boat will move back and forth within

a particular distance. D. The boat will move in

the direction opposite to the flow of water.

Forces in One Dimension

CHAPTER4

Chapter Assessment

Reason Since two equal and opposite forces are

acting together, the net force is zero. Hence,

the boat will not move at all.

Forces in One Dimension

CHAPTER4

Chapter Assessment

- What is inertia?

A. Force. B. The tendency of a body to stay

only at rest C. The tendency of a body to move

with constant acceleration D. The tendency of a

body to move with constant velocity

Forces in One Dimension

CHAPTER4

Chapter Assessment

- Reason Inertia of a body is the tendency of a

body to stay at rest and/or to move with a

constant velocity. Remember being at rest is

simply a special case of constant velocity, v 0

m/s.

Forces in One Dimension

CHAPTER4

Chapter Assessment

- If the weight of a person on Earth is 120 N, what

will his weight be on the Moon? (Gravity on the

Moon is six times less than the gravity on Earth.)

Forces in One Dimension

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Chapter Assessment

Reason Gravity on the Moon is .

Forces in One Dimension

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Chapter Assessment

Reason

Weight of person on the Moon

Gravity on the Moon

mass of person

Forces in One Dimension

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Chapter Assessment

- What happens when the drag force is equal to the

force of gravity?

A. The object comes to rest. B. The object

moves with constant acceleration. C. The object

moves with constant velocity. D. The velocity of

the object increases.

Forces in One Dimension

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Chapter Assessment

Reason When drag force equals the force due to

gravity, the net force acting on the object is

zero. As a result of this, the object moves with

constant velocity, which is called terminal

velocity.

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Standardized Test Practice

- What is the acceleration of the car described by

the graph on the right?

A. 0.20 m/s2 B. 0.40 m/s2

C. 1.0 m/s2 D. 2.5 m/s2

Forces in One Dimension

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Standardized Test Practice

- What distance will the car described by the above

graph have traveled after 4.0 s?

A. 13 m B. 40 m

C. 80 m D. 90 m

Forces in One Dimension

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Standardized Test Practice

- If the car in the graph on the right maintains a

constant acceleration, what will its velocity be

after 10 s.

A. 10 km/h B. 25 km/h

C. 90 km/h D. 120 km/h

Forces in One Dimension

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Standardized Test Practice

- In a tug-of-war, 13 children, with an average

mass of 30 kg each, pull westward on a rope with

an average force of 150 N per child. Five

parents, with an average mass of 60 kg each, pull

eastward on the other end of the rope with an

average force of 475 N per adult. Assuming that

the whole mass accelerates together as a single

entity, what is the acceleration of the system?

A. 0.62 m/s2 E B. 2.8 m/s2 W

C. 3.4 m/s2 E D. 6.3 m/s2 W

Forces in One Dimension

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Standardized Test Practice

- What is the weight of a 225-kg space probe on the

Moon? The acceleration of gravity on the Moon is

1.62 m/s2.

A. 139 N B. 364 N C. 1.35103 N D. 2.21103 N

Forces in One Dimension

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Standardized Test Practice

Test-Taking Tip

- Maximize Your Score

If possible, find out how your standardized test

will be scored. In order to do your best, you

need to know if there is a penalty for guessing,

and if so, what the penalty is. If there is no

random-guessing penalty at all, you should always

fill in an answer, even if you have not read the

question.

Forces in One Dimension

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Chapter Resources

Forces Exerted on the Book

Forces in One Dimension

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Chapter Resources

Ball Tied to a String

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Chapter Resources

Ball Held in Your Hand

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Chapter Resources

The Carts Motion Shown in a Linear Relationship

Forces in One Dimension

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Chapter Resources

Acceleration of Cart

Forces in One Dimension

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Chapter Resources

Force-Acceleration Graph

Forces in One Dimension

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Chapter Resources

Combining Forces

Forces in One Dimension

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Chapter Resources

Fighting Over a Toy

Forces in One Dimension

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Chapter Resources

An Elevator Accelerating Upward

Forces in One Dimension

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Chapter Resources

A Soccer Ball on a Table on Earth

Forces in One Dimension

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Chapter Resources

Earths Acceleration

Forces in One Dimension

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Chapter Resources

The Normal Force on an Object

End of Custom Shows