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 5: Work and Energy

Section 1: Work

Section 2: Energy

Section 3: Conservation of Energy

Section 4: Power

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 5: Work and Energy Classwork/Homework Packet

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Chapter 5.1: Work (pp. 154-157)

Practice A, pp. 155-156 #1-4

Work

Due: _________________

1. A tugboat pulls a ship with a constant net horizontal force of 5.00 × 103 N and causes the

ship to move through a harbor. How much work is done on the ship if it moves a distance of

3.00 km?

2. A weight lifter lifts a set of weights a vertical distance of 2.00 m. If a constant net force of

350 N is exerted on the weights, what is the net work done on the weights?

3. A shopper in a supermarket pushes a cart with a force of 35 N directed at an angle of 25°

downward from the horizontal. Find the work done by the shopper on the cart as the

shopper moves along a 50.0 m length of aisle.

4. If 2.0 J of work is done in raising a 180 g apple, how far is it lifted?





Chapter 5.1: Work (pp. 154-157)

Formative Assessment 5.1, p. 157 #1-6

Due: _________________

1. For each of the following cases, indicate whether the work done on the second object in

each example will have a positive or a negative value.

a. The road exerts a friction force on a speeding car skidding to a stop.

b. A rope exerts a force on a bucket as the bucket is raised up a well.

c. Air exerts a force on a parachute as the parachutist falls to Earth.

2. If a neighbor pushes a lawnmower four times as far as you do but exerts only half the force,

which one of you does more work and by how much?

3. A worker pushes a 1.50 × 103 N crate with a horizontal force of 345 N a distance of 24.0 m.

Assume the coefficient of kinetic friction between the crate and the floor is 0.220.

a. How much work is done by the worker on the crate?

b. How much work is done by the floor on the crate?

c. What is the net work done on the crate?





4. A 0.075 kg ball in a kinetic sculpture moves at a constant speed along a motorized vertical

conveyor belt. The ball rises 1.32 m above the ground. A constant frictional force of 0.350 N

acts in the direction opposite the conveyor belt’s motion. What is the net work done on the

ball?

5. Critical Thinking For each of the following statements, identify whether the everyday or the

scientific meaning of work is intended.

a. Jack had to work against time as the deadline neared.

b. Jill had to work on her homework before she went to bed.

c. Jack did work carrying the pail of water up the hill.

6. Critical Thinking Determine whether work is being done in each of the following examples:

a. a train engine pulling a loaded boxcar initially at rest

b. a tug of war that is evenly matched

c. a crane lifting a car





Chapter 5.2: Energy (pp. 158-166)

Practice B, pp. 159-160 #1-5

Kinetic Energy

Due: _________________

1. Calculate the speed of an 8.0 × 104 kg airliner with a kinetic energy of 1.1 × 109 J.

2. What is the speed of a 0.145 kg baseball if its kinetic energy is 109 J?

3. Two bullets have masses of 3.0 g and 6.0 g, respectively. Both are fired with a speed of 40.0

m/s. Which bullet has more kinetic energy? What is the ratio of their kinetic energies?

4. Two 3.0 g bullets are fired with speeds of 40.0 m/s and 80.0 m/s, respectively. What are

their kinetic energies? Which bullet has more kinetic energy? What is the ratio of their

kinetic energies?

5. A car has a kinetic energy of 4.32 × 105 J when traveling at a speed of 23 m/s. What is its

mass?






Practice C, pp. 161-162 #1-4

Work-Kinetic Energy Theorem

Due: _________________

1. A student wearing frictionless in-line skates on a horizontal surface is pushed by a friend

with a constant force of 45 N. How far must the student be pushed, starting from rest, so

that her final kinetic energy is 352 J?

2. A 2.0 × 103 kg car accelerates from rest under the actions of two forces. One is a forward

force of 1140 N provided by traction between the wheels and the road. The other is a 950 N

resistive force due to various frictional forces. Use the work–kinetic energy theorem to

determine how far the car must travel for its speed to reach 2.0 m/s.





3. A 2.1 × 103 kg car starts from rest at the top of a driveway that is sloped at an angle of 20.0°

with the horizontal. An average friction force of 4.0 × 103 N impedes the car’s motion so that

the car’s speed at the bottom of the driveway is 3.8 m/s. What is the length of the driveway?

4. A 75 kg bobsled is pushed along a horizontal surface by two athletes. After the bobsled is

pushed a distance of 4.5 m starting from rest, its speed is 6.0 m/s. Find the magnitude of the

net force on the bobsled.






Practice D, pp. 165-166 #1-3

Potential Energy

Due: _________________

1. A spring with a force constant (a.k.a. spring constant) of 5.2 N/m has a relaxed length of 2.45

m. When a mass is attached to the end of the spring and allowed to come to rest, the

vertical length of the spring is 3.57 m. Calculate the elastic potential energy stored in the

spring.

2. The staples inside a stapler are kept in place by a spring with a relaxed length of 0.115 m. If

the spring constant is 51.0 N/m, how much elastic potential energy is stored in the spring

when its length is 0.150 m?

3. A 40.0 kg child is in a swing that is attached to ropes 2.00 m long. Find the gravitational

potential energy associated with the child relative to the child’s lowest position under the

following conditions:

a. when the ropes are horizontal

b. when the ropes make a 30.0° angle with the vertical

c. at the bottom of the circular arc







Due: _________________

1. A pinball bangs against a bumper, giving the ball a speed of 42 cm/s. If the ball has a mass of

50.0 g, what is the ball’s kinetic energy in joules?

2. A student slides a 0.75 kg textbook across a table, and it comes to rest after traveling 1.2 m.

Given that the coefficient of kinetic friction between the book and the table is 0.34, use the

work–kinetic energy theorem to find the book’s initial speed.





3. A spoon is raised 21.0 cm above a table. If the spoon and its contents have a mass of 30.0 g,

what is the gravitational potential energy associated with the spoon at that height relative to

the surface of the table?

4. Critical Thinking What forms of energy are involved in the following situations?

a. a bicycle coasting along a level road

b. heating water

c. throwing a football

d. winding the mainspring of a clock

5. Critical Thinking How do the forms of energy in item 4 differ from one another? Be sure to

discuss mechanical versus nonmechanical energy, kinetic versus potential energy, and

gravitational versus elastic potential energy.





Chapter 5.3: Conservation of Energy (pp. 167-172)

Practice E, pp. 170-171 #1-5

Conservation of Mechanical Energy

Due: _________________

1. A bird is flying with a speed of 18.0 m/s over water when it accidentally drops a 2.00 kg fish.

If the altitude of the bird is 5.40 m and friction is disregarded, what is the speed of the fish

when it hits the water?

2. A 755 N diver drops from a board 10.0 m above the water’s surface. Find the diver’s speed

5.00 m above the water’s surface. Then find the diver’s speed just before striking the water.





3. If the diver in item 2 leaves the board with an initial upward speed of 2.00 m/s, find the

diver’s speed when striking the water.

4. An Olympic runner leaps over a hurdle. If the runner’s initial vertical speed is 2.2 m/s, how

much will the runner’s center of mass be raised during the jump?

5. A pendulum bob is released from some initial height such that the speed of the bob at the

bottom of the swing is 1.9 m/s. What is the initial height of the bob?





Chapter 5.3: Conservation of Energy (pp. 167-172)


Due: _________________

1. If the spring of a jack-in-the-box is compressed a distance of 8.00 cm from

its relaxed length and then released, what is the speed of the toy head

when the spring returns to its natural length? Assume the mass of the toy

head is 50.0 g, the spring constant is 80.0 N/m, and the toy head moves

only in the vertical direction. Also disregard the mass of the spring. (Hint:

Remember that there are two forms of potential energy in the problem.)

2. You are designing a roller coaster in which a car will be pulled to the top of a hill of height h

and then, starting from a momentary rest, will be released to roll freely down the hill and

toward the peak of the next hill, which is 1.1 times as high. Will your design be successful?

Explain your answer.





3. Is conservation of mechanical energy likely to hold in these situations?

a. a hockey puck sliding on a frictionless surface of ice

b. a toy car rolling on a carpeted floor

c. a baseball being thrown into the air

4. Critical Thinking What parts of the kinetic sculpture on the opening pages of this chapter

involve the conversion of one form of energy to another? Is mechanical energy conserved in

these processes?





Chapter 5.4: Power (pp. 173-175)

Practice F, pp. 174-175 #1-5

Power

Due: _________________

1. A 1.0 × 103 kg elevator carries a maximum load of 800.0 kg. A constant frictional force of

4.0 × 103 N retards the elevator’s motion upward. What minimum power, in kilowatts, must

the motor deliver to lift the fully loaded elevator at a constant speed of 3.00 m/s?

2. A car with a mass of 1.50 × 103 kg starts from rest and accelerates to a speed of 18.0 m/s in

12.0 s. Assume that the force of resistance remains constant at 400.0 N during this time.

What is the average power developed by the car’s engine?

3. A rain cloud contains 2.66 × 107 kg of water vapor. How long would it take for a 2.00 kW

pump to raise the same amount of water to the cloud’s altitude, 2.00 km?

4. How long does it take a 19 kW steam engine to do 6.8 × 107 J of work?

5. A 1.50 × 103 kg car accelerates uniformly from rest to 10.0 m/s in 3.00 s.

a. What is the work done on the car in this time interval?

b. What is the power delivered by the engine in this time interval?





Chapter 5.4: Power (pp. 173-175)


Due: _________________

1. A 50.0 kg student climbs 5.00 m up a rope at a constant speed. If the student’s power output

is 200.0 W, how long does it take the student to climb the rope? How much work does the

student do?

2. A motor-driven winch pulls the 50.0 kg student in the previous item 5.00 m up the rope at a

constant speed of 1.25 m/s. How much power does the motor use in raising the student?

How much work does the motor do on the student?

3. Critical Thinking How are energy, time, and power related?

4. Critical Thinking People often use the word powerful to describe the engines in some

automobiles. In this context, how does the word relate to the definition of power? How does

this word relate to the alternative definition of power?





Chapter 5 Review (pp. 180-185)


































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Mr. Stephen Dobosh’s EP-M 4 Physics Classwork/Homework...

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