mr. stephen dobosh’s ep-m 4 physics classwork/homework...

Assumption College English Program

Mr. Stephen Dobosh’s

E P - M 4 P h y s i c s C l a s s w o r k / H o m e w o r k P a c k e t

Chapter 4: Forces and the Laws of Motion

Section 1: Changes in Motion

Section 2: Newton’s First Law

Section 3: Newton’s Second and Third Laws

Section 4: Everyday Forces

Student’s Name ……………………..…………………..…… EP-M …./…. ID #………….. Register #……

Much of the material within this packet is drawn from the course textbook Holt Physics that each of you have purchased. This content is copyrighted © 2012 by Holt McDougal, a division of Houghton Mifflin Harcourt Publishing Company. No part of this work may be

reproduced or transmitted in any form without prior written permission of the copyright owner.

Chapter 4: Forces and the Laws of Motion Classwork/Homework Packet

Mr. Stephen Dobosh of 32

Questions? Come see Mr. Steve or email him with a picture of your work at [email protected].

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EQUATION SHEET





In-Class Free-Body Diagram Practice

1. An acrobat is suspended motionless from the ceiling by a rope. Fr

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2. An egg is free-falling from a nest in a tree. Neglect air resistance.

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3. An egg is falling (not freely, do not neglect air resistance) from a nest in a tree.

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5. A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance.

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6. A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance.

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7. A Bangkok taxi is (actually) stopping at a red light.

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8. A skydiver is descending with a constant velocity. Of course, consider air resistance.

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9. A car is parked on a sloped street.

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10. A hot air balloon is accelerating upward.

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11. A car is coasting to the right and slowing down.

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12. A soccer ball while being kicked at a 45° angle.

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13. A soccer ball that has already been kicked at a 45° angle.

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14. A race car crashing head-on into a brick wall.

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Chapter 4.1: Changes in Motion (pp. 118-122)

Practice A, pp. 121-122 #1-2

Drawing Free-Body Diagrams

Due: _________________

1. A truck pulls a trailer on a flat stretch of road. The forces acting on the trailer are the force

due to gravity (250 000 N downward), the force exerted by the cable connecting the trailer

to the truck (20 000 N to the right). The forces acting on the truck are the force due to

gravity (80 000 N downward), the force exerted by the road (80 000 N upward), the force

exerted by the cable (20 000 N to the left), and the force causing the truck to move forward

26 400 N to the right).

a. Draw and label a free-body diagram of the trailer.

b. Draw and label a free-body diagram of the truck.

2. A physics book is at rest on a desk. Gravitational force pulls the book down. The desk exerts

an upward force on the book that is equal in magnitude to the gravitational force. Draw a

free-body diagram of the book.

Note: You can draw one, single

diagram of both if you like.





Chapter 4.1: Changes in Motion (pp. 118-122)

Formative Assessment 4.1, p. 122 #1-6

Due: _________________

1. List three examples of each of the following:

a. a force causing an object to start moving

b. a force causing an object to stop moving

c. a force causing an object to change its direction of motion

2. Give two examples of field forces described in this section and two examples of contact

forces you observe in everyday life. Explain why you think that these are forces.

3. What is the SI unit of force? What is this unit equivalent to in terms of fundamental units?

4. Why is force a vector quantity?

5. Draw a free-body diagram of a football being kicked. Assume that the only forces acting on

the ball are the force due to gravity and the force exerted by the kicker.





6. Interpreting Graphics Study the force diagram shown (Holt 2009 ed., Figure 3(a)). Redraw

the diagram, and label each vector arrow with a description of the force. In each description,

include the object exerting the force and the object on which the force is acting.





Chapter 4.2: Newton’s First Law (pp. 123-127)

Practice B, pp. 125-126 #1-3

Determining Net Force

Due: _________________

1. A man is pulling on his dog with a force of 70.0 N directed at an angle of +30.0° to the

horizontal. Find the x and y components of this force.

2. A gust of wind blows an apple from a tree. As the apple falls, the gravitational force on the

apple is 2.25 N downward, and the force of the wind on the apple is 1.05 N to the right. Find

the magnitude and direction of the net force on the apple.

3. The wind exerts a force of 452 N north on a sailboat, while the water exerts a force of 325 N

west on the sailboat. Find the magnitude and direction of the net force on the sailboat.





Chapter 4.2: Newton’s First Law (pp. 123-127)


Due: _________________

1. If a car is traveling westward with a constant velocity of 20 m/s, what is the net force acting

on the car?

2. If a car is accelerating downhill under a net force of 3674 N, what additional force would

cause the car to have a constant velocity?

3. The sensor in the torso of a crash-test dummy records the magnitude and direction of the

net force acting on the dummy. If the dummy is thrown forward with a force of 130.0 N

while simultaneously being hit from the side with a force of 4500.0 N, what force will the

sensor report?

4. What force will the seat belt have to exert on the dummy in item 3 to hold the dummy in the

seat?

5. Critical Thinking Can an object be in equilibrium if only one force acts on the object?





Chapter 4.3: Newton’s Second and Third Laws (pp. 128-132)

Practice C, pp. 129-130 #1-5

Newton’s Second Law

Due: _________________

1. The net force on the propeller of a 3.2 kg model airplane is 7.0 N forward. What is the

acceleration of the airplane?

2. The net force on a golf cart is 390 N north. If the cart has a total mass of 270 kg, what are the

magnitude and direction of the cart’s acceleration?

3. A car has a mass of 1.50 × 103 kg. If the force acting on the car is 6.75 × 103 N to the east,

what is the car’s acceleration?

4. A soccer ball kicked with a force of 13.5 N accelerates at 6.5 m/s2 to the right. What is the

mass of the ball?

5. A 2.0 kg otter starts from rest at the top of a muddy incline 85 cm long and slides down to

the bottom in 0.50 s. What net force acts on the otter along the incline?





Chapter 4.3: Newton’s Second and Third Laws (pp. 128-132)


Due: _________________

1. A 6.0 kg object undergoes an acceleration of 2.0 m/s2.

a. What is the magnitude of the net force acting on the object?

b. If this same force is applied to a 4.0 kg object, what acceleration is produced?

2. A child causes a wagon to accelerate by pulling it with a horizontal force. Newton’s third law

says that the wagon exerts an equal and opposite force on the child. How can the wagon

accelerate? (Hint: Draw a free-body diagram for each object.)

3. Identify the action-reaction pairs in the following situations:

a. A person takes a step.

b. A snowball hits someone in the back.

c. A baseball player catches a ball.

d. A gust of wind strikes a window.





4. The forces acting on a sailboat are 390 N north and 180 N east. If the boat (including crew)

has a mass of 270 kg, what are the magnitude and direction of the boat’s acceleration?

5. Critical Thinking If a small sports car collides head-on with a massive truck, which vehicle

experiences the greater impact force? Which vehicle experiences the greater acceleration?

Explain your answers.





Chapter 4.4: Everyday Forces (pp. 133-141)

Practice D, p. 137 #1-3

Coefficients of Friction

Due: _________________

1. Once the crate in Sample Problem D is in motion, a horizontal force of 53 N keeps the crate

moving with a constant velocity. Find µk, the coefficient of kinetic friction, between the crate

and the floor.

2. A 25 kg chair initially at rest on a horizontal floor requires a 165 N horizontal force to set it in

motion. Once the chair is in motion, a 127 N horizontal force keeps it moving at a constant

velocity.

a. Find the coefficient of static friction between the chair and the floor.

b. Find the coefficient of kinetic friction between the chair and the floor.





3. A museum curator moves artifacts into place on various different display surfaces. Use the

values in Figure 4.7 (Holt 2009 ed., Table 2) to find Fs,max and Fk for the following situations:

a. moving a 145 kg aluminum sculpture across a horizontal steel platform

b. pulling a 15 kg steel sword across a horizontal steel shield

c. pushing a 250 kg wood bed on a horizontal wood floor

d. sliding a 0.55 kg glass amulet on a horizontal glass display case






Practice E, p. 138-139 #1-4

Overcoming Friction

Due: _________________

1. A student pulls on a rope attached to a box of books and moves the box down the hall. The

student pulls with a force of 185 N at an angle of 25.0° above the horizontal. The box has a

mass of 35.0 kg, and µk between the box and the floor is 0.27. Find the acceleration of the

box.

2. The student in item 1 moves the box up a ramp inclined at 12° with the horizontal. If the box

starts from rest at the bottom of the ramp and is pulled at an angle of 25.0° with respect to

the incline and with the same 185 N force, what is the acceleration up the ramp? Assume

that µk = 0.27.





3. A 75 kg box slides down a 25.0° ramp with an acceleration of 3.60 m/s2.

a. Find µk between the box and the ramp.

b. What acceleration would a 175 kg box have on this ramp?

4. A box of books weighing 325 N moves at a constant velocity across the floor when the box is

pushed with a force of 425 N exerted downward at an angle of 35.2° below the horizontal.

Find µk between the box and the floor.







Due: _________________

1. Draw a free-body diagram for each of the following objects:

a. a projectile accelerating downward in the presence of air resistance

b. a crate being pushed across a flat surface at a constant speed

2. A bag of sugar has a mass of 2.26 kg.

a. What is its weight in newtons on the moon, where the acceleration due to gravity is

one-sixth that on Earth?

b. What is its weight on Jupiter, where the acceleration due to gravity is 2.64 times

that on Earth?





3. A 2.0 kg block on an incline at a 60.0° angle is held in equilibrium by a horizontal force.

a. Determine the magnitude of this horizontal force. (Disregard friction.)

b. Determine the magnitude of the normal force on the block.

4. A 55 kg ice skater is at rest on a flat skating rink. A 198 N horizontal force is needed to set

the skater in motion. However, after the skater is in motion, a horizontal force of 175 N

keeps the skater moving at a constant velocity. Find the coefficients of static and kinetic

friction between the skates and the ice.

5. Critical Thinking The force of air resistance acting on a certain falling object is roughly

proportional to the square of the object’s velocity and is directed upward. If the object falls

fast enough, will the force of air resistance eventually exceed the weight of the object and

cause the object to move upward? Explain.





Chapter 4 Review (pp. 143-147)


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