SPH3U Exam Review

Work

1. The work done on a system is equal to its change in:

A. force

B. energy

C. power

D. both B and C

Work

1. The work done on a system is equal to its change in:

A. force

*B. energy

C. power

D. both B and C

Units

2. Energy may be measured in:

A. Joules

B. calories

C. kilowatt-hours

D. all of the above

Units

2. Energy may be measured in:

A. Joules

B. calories

C. kilowatt-hours

*D. all of the above

Total Mechanical Energy

3. An object is lifted to some height and then dropped. While it is being lifted, its total mechanical energy:

A. increases

B. decreases

C. remains the same

D. It cannot be determined.

Total Mechanical Energy

3. An object is lifted to some height and then dropped. While it is being lifted, its total mechanical energy:

*A. increases

B. decreases

C. remains the same

D. It cannot be determined.

Total Mechanical Energy

4. An object is lifted to some height and then dropped. During the drop, its total mechanical energy:

A. increases

B. decreases

C. remains the same

D. It cannot be determined.

Total Mechanical Energy

4. An object is lifted to some height and then dropped. During the drop, its total mechanical energy:

A. increases

B. decreases

*C. remains the same

D. It cannot be determined.

Work and Friction

5. A student uses a force of 20 N to push a book 1.0 m along a table. A frictional force of 20 N opposes the motion of the book. The work done by the student is:

A. 0 J B. 20 J C. 40 J D. It cannot be determined.

Work and Friction

5. A student uses a force of 20 N to push a book 1.0 m along a table. A frictional force of 20 N opposes the motion of the book. The work done by the student is:

A. 0 J *B. 20 J C. 40 J D. It cannot be determined.

Power

6. Machine A does 10 J of work in 1 s. Machine B does 10 J of work in 2 s. Which machine has the greatest power output?

A. Machine A B. Machine B C. Their outputs are the same. D. It cannot be determined.

Power

6. Machine A does 10 J of work in 1 s. Machine B does 10 J of work in 2 s. Which machine has the greatest power output?

*A. Machine A B. Machine B C. Their outputs are the same. D. It cannot be determined.

Efficiency

7. Machine C uses 2500 J of fuel energy to do 500 J of useful work. Its efficiency is:

A. 0%

B. 20%

C. 100%

D. 500%

Efficiency

7. Machine C uses 2500 J of fuel energy to do 500 J of useful work. Its efficiency is:

A. 0%

*B. 20%

C. 100%

D. 500%

Energy Loss

8. The 2000 J of energy lost in the Question 7 was probably lost as ______ energy.

A. elastic potential

B. gravitational potential

C. heat

D. kinetic

Energy Loss

8. The 2000 J of energy lost in the Question 7 was probably lost as ______ energy.

A. elastic potential

B. gravitational potential

*C. heat

D. kinetic

Heat Exchange

9. If 100 g of water at 100oC is added to a 50 g aluminum cup at 20oC:

A. The temperature change of the water will be the same as the temperature change of the cup.

B. The temperature change of the water will be less than the temperature change of the cup.

C. The temperature change of the water will be greater than the temperature change of the cup.

D. No transfer of heat energy will occur between the materials.

Heat Exchange

9. If 100 g of water at 100oC is added to a 50 g aluminum cup at 20oC:

A. The temperature change of the water will be the same as the temperature change of the cup.

*B. The temperature change of the water will be less than the temperature change of the cup.

C. The temperature change of the water will be greater than the temperature change of the cup.

D. No transfer of heat energy will occur between the materials.

Heat Transfer

10. Which of the following processes is most effective at transferring heat energy within fluids?

A. conduction

B. convection

C. radiation

D. all of the above

Heat Transfer

10. Which of the following processes is most effective at transferring heat energy within fluids?

A. conduction

*B. convection

C. radiation

D. all of the above

Energy Transformations

1. A textbook is dropped from some height onto the floor. Explain, using energy transformations, why and how the book stops when it hits the floor.

Energy Transformations

1. A textbook is dropped from some height onto the floor. Explain, using energy transformations, why and how the book stops when it hits the floor.

The floor does negative work on the book by exerting a normal force opposite the direction of motion.

Entropy

2. Explain what is meant by “entropy” and how the concept applies to the transformation of mechanical energy.

Entropy is the disorder of a system. As energy is transferred, some is lost as non-useful forms, so the entropy of the system is increased.

Problem Solving 1

1. A student applies a force of magnitude 39.0 N at an angle of 22.6o with the horizontal to push a 4.00-kg textbook 1.00 m across a table to a final speed of 1.75 m/s. Find the work done by friction on the textbook.

Problem Solving 1

1. A student applies a force of magnitude 39.0 N at an angle of 22.6o with the horizontal to push a 4.00-kg textbook 1.00 m across a table to a final speed of 1.75 m/s. Find the work done by friction on the textbook.

JW

mNW

dFW

student

student

student

0.36

6.22cos)00.1)(0.39(

cos

Problem Solving 1

1. A student applies a force of magnitude 39.0 N at an angle of 22.6o with the horizontal to push a 4.00-kg textbook 1.00 m across a table to a final speed of 1.75 m/s. Find the work done by friction on the textbook.

JE

kgE

mvE

k

sm

k

k

125.6

)75.1)(00.4( 221

221

Problem Solving 1

1. A student applies a force of magnitude 39.0 N at an angle of 22.6o with the horizontal to push a 4.00-kg textbook 1.00 m across a table to a final speed of 1.75 m/s. Find the work done by friction on the textbook.

JW

JJW

WEWWWE

friction

friction

studentkfrictionfrictionstudentk

9.29

0.36125.6

Problem Solving 2

2. 3.0-kg parcels are lifted up to the top of a 5.0-m high ramp. If 24 parcels are lifted every minute, what power is required to lift the parcels? If this power is supplied by a 12 kW motor, what is the efficiency of the motor?

Problem Solving 2

2. 3.0-kg parcels are lifted up to the top of a 5.0-m high ramp. If 24 parcels are lifted every minute, what power is required to lift the parcels?

Problem Solving 2

2. 3.0-kg parcels are lifted up to the top of a 5.0-m high ramp. If 24 parcels are lifted every minute, what power is required to lift the parcels?

WP

s

mkgP

t

hmg

t

E

t

WP

sm

8.58

60

)0.5)(8.9)(0.3(24 2

Problem Solving 2

If this power is supplied by a 12 kW motor, what is the efficiency of the motor?

%49.00049.012000

8.58or

W

Wefficiency

P

Pefficiency

in

out