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.
Wstudent  Fd cos
Wstudent  (39.0 N )(1.00 m) cos 22.6
Wstudent  36.0 J
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.
Ek  12 m v2
Ek  12 (4.00 kg )(1.75 ms ) 2
Ek  6.125 J
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.
Ek  Wstudent  W friction  W friction  Ek  Wstudent
W friction  6.125J  36.0 J
W friction  29.9 J
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?
W E m gh
P


t t
t
24(3.0kg )(9.8 sm2 )(5.0 m)
P
60 s
P  58.8W
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?
W E m gh
P


t t
t
24(3.0kg )(9.8 sm2 )(5.0 m)
P
60 s
P  58.8W
Problem Solving 2
If this power is supplied by a 12 kW motor,
what is the efficiency of the motor?
Pout
efficiency 
Pin
58.8W
efficiency 
 0.0049or 0.49%
12000W