Name: _______________________________________
Class: ______________
AST/SE
All Questions
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Date: ___________
ANSWER KEY
Different forms of energy
Checkup
1 WHAT IS ENERGY? (pp. 70–78)
1. Name the form or forms of energy in each of the following energy sources.
A
B
Chemical energy.
Chemical energy.
D
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C
Elastic energy.
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Radiation energy.
1
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Name: _______________________________________
Class: ______________
Date: ___________
2. In each of the following examples, is energy used to do work or to cause a change?
a) a puddle of water evaporating in the sun
A change.
b) a burning log
A change.
c) a car moving along the road
Work.
d) a person climbing a staircase
Work.
3. Why is the amount of energy in the universe said to be constant?
Because, according to the law of conservation of energy, energy is neither created nor destroyed. The
total amount of energy therefore remains constant.
4. Does each of the following situations describe a transfer or a transformation of energy, or
both?
a) Solar energy makes photosynthesis in plants possible.
A transformation of energy.
b) Energy from a heating system warms the air in a home.
A transfer of energy.
c) Power plants generate electricity that is then delivered to our homes.
A transformation and a transfer of energy.
d) Food provides the energy we need to go about our daily lives.
A transformation of energy.
5. To perform work equal to 2 400 J, a machine consumes 12 000 J. What is the energy
efficiency of this machine?
=
Useful energy
Energy consumed
2 400 J
12 000 J
× 100
× 100 = 20%
6. Can a cup of boiling water contain more thermal energy than a bucket of water at 50°C?
Explain your answer.
Not necessarily, because heat depends not only on the temperature but also on the amount of matter
involved.
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2
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Energy efficiency =
Name: _______________________________________
Class: ______________
Date: ___________
7. Amanda applies the same amount of heat to four samples of matter:
– a piece of wood
– a piece of silver
– a piece of iron
– a piece of copper
If each sample has the same mass and the same initial temperature, which will experience the
greatest temperature variation? Explain your answer.
The piece of silver will experience the greatest temperature variation because its specific heat capacity
is the lowest. It therefore takes less energy to increase the temperature of the silver by 1°C than to raise
the temperature of the other samples.
8. Ravi puts a 100-g block of lead, heated to 155°C, in 100 mL of water at 19°C. The water
temperature rises to 24°C. Assuming no energy has been lost to the surroundings, calculate
the specific heat capacity of lead.
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Problem-solving steps
Application
1. Determine what you are looking for.
How much heat is released by the lead and then
absorbed by the water?
2. Determine the different variables and their
respective values.
Q
m
c
∆T
3. Choose the appropriate formula.
Q = mc∆T
4. Replace each variable by its value and isolate
the unknown variable.
Q = 100 g × 4.19 J/g°C × 5°C
= 2095 J
5. Check your solution and answer the problem
question.
The water absorbed 2095 J of heat. Therefore,
the heat released by the lead equals −2095 J.
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=?
= 100 g
= 4.19 J/g°C
= 24°C – 19°C = 5°C
3
ANSWER KEY
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Different forms of energy
Name: _______________________________________
Class: ______________
Problem-solving steps
Date: ___________
Application
1. Determine what you are looking for.
What is the specific heat capacity of lead?
2. Determine the different variables and their
respective values.
Q
m
c
∆T
3. Choose the appropriate formula.
Q = mc∆T
4. Replace each variable by its value and isolate
the unknown variable.
c=
5. Check your solution and answer the problem
question.
The specific heat capacity of lead is
0.16 J/g°C.
= –2095 J
= 100 g
=?
= 24°C – 155°C = –131°C
–2095 J
100 g × –131°C
= 0.16 J/g°C
9. You pour 250 mL of water into a glass just out of the freezer. After a while, you notice that the
temperature of the water has fallen from 18°C to 12°C.
a) How much heat has been transferred between the water and the glass?
Problem-solving steps
Application
How much heat was transferred between the
water and the glass?
2. Determine the different variables and their
respective values.
Q
m
c
∆T
3. Choose the appropriate formula.
Q = mc∆T
4. Replace each variable by its value and
isolate the unknown variable.
Q = 250 g × 4.19 J/g°C × –6°C
= –6285 J
CHAPTER 3
Different forms of energy
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1. Determine what you are looking for.
=?
= 250 g
= 4.19 J/g°C
= 12°C – 18°C = –6°C
4
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5. Check your solution and answer the
problem question.
Class: ______________
Date: ___________
A total of –6285 J of heat was transferred between
the water and the glass.
b) Did the water give off or absorb energy? Explain your answer.
The water gave off energy because its temperature dropped.
c) Did the glass give off or absorb energy? Explain your answer.
The glass absorbed energy because heat always passes from the warmer to the cooler
environment.
10. A baseball pitcher throws a ball weighing about 150 g to another player. What is the kinetic
energy of the ball if, at the moment it is caught, its velocity is 5 m/s?
Problem-solving steps
Application
1. Determine what you are looking for.
What is the kinetic energy of the ball?
2. Determine the different variables and their
respective values.
Ek = ?
m = 0.150 kg
v = 5 m/s
3. Choose the appropriate formula.
Ek =
1
mv2
2
1
4. Replace each variable by its value and isolate
× 0.150 kg × (5 m/s)2
Ek =
2
the unknown variable.
= 1.875 J
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5. Check your solution and answer the problem
question.
The kinetic energy of the ball at the moment it
is caught is 1.875 J.
11. An elevator carries a person weighing 60 kg from the ground to the eighth floor.
a) If the eighth floor is 56 m above the ground, what is the potential energy acquired by
the person?
Problem-solving steps
Application
1. Determine what you are looking
for.
What is the potential energy acquired by the person?
2. Determine the different variables
and their respective values.
Ep
m
g
h
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=?
= 60 kg
= 9.8 N/kg
= 56 m
5
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Name: _______________________________________
Class: ______________
Date: ___________
3. Choose the appropriate
formula.
Ep = mgh
4. Replace each variable by its
value and isolate the unknown
variable.
Ep = 60 kg × 9.8 N/kg × 56 m
Ep = 32 928 J
5. Check your solution and answer
the problem question.
The potential energy acquired by the person is 32 928 J.
b) Where did the potential energy come from?
It came from the work done by the elevator.
12. Jessica builds a model track for her little brother.
She places a toy bus weighing 0.5 kg at point A
and gives it a velocity of 2 m/s. The bus travels
the entire route with no further addition of energy.
a) Ignoring the effect of friction, calculate the
mechanical energy, the potential energy and the
kinetic energy of the bus at points A, B and C.
At point A
At point B
At point C
Em = 3.45 J
Em = 3.45 J
1
mv2
2
1
Ep = 0.5 kg × 9.8 N/kg × 0.1 m Ek =
× 0.5 kg × (3 m/s)2
1
2
2
=
× 0.5 kg × (2 m/s) = 1 J
= 0.49 J
= 2.25 J
2
Ep = mgh
Ek = 3.45 J – 0.49 J
Ep = 3.45 J – 2.25 J
= 2.96 J
= 0.5 kg × 9.8 N/kg × 0.5 m
= 1.2 J
= 2.45 J
Ek =
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Em = Ek + Ep
= 1 J + 2.45 J
= 3.45 J
b) Calculate the height of the bus at point C.
Ep = mgh
1.2 J = 0.5 kg × 9.8 N/kg × h
h=
1.2 J
0.5 kg × 9.8 N/kg
h = 0.245 m
CHAPTER 3
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6
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2 MOTION AND FORCES (pp. 79–91)
13. In each of the following situations, does the force involve pulling or pushing?
a) the force of a dog on its leash
Pulling.
b) the force of a person inserting a letter in an envelope
Pushing.
c) the force of a magnet on a paper clip
Pulling.
d) the force of a bowstring on an arrow
Pushing.
14. The illustration opposite represents the action of a force.
a) Is the force applied horizontally or vertically?
The force is applied at an angle of 25° to the
horizontal.
b) Which symbol indicates the direction of the force?
The arrowhead.
c) What is the magnitude of the force?
20 N.
15. How does the intensity of the Earth’s gravitational field vary?
The intensity of the Earth’s gravitational field decreases as the distance from the centre of the Earth
increases.
16. What distinguishes mass from weight?
Mass is a measure of the quantity of matter in an object, while weight is a measure of the
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gravitational force acting on an object.
17. Plasma or liquid crystal television sets are much lighter in weight than the old models with
cathode ray screens. What is the weight of a television set that has a mass of 25 kg at the
Earth’s surface?
Problem-solving steps
Application
1. Determine what you are looking for.
What is the weight of the object?
2. Determine the different variables and their
respective values.
Fg = ?
m = 25 kg
g = 9.8 N/kg
3. Choose the appropriate formula.
Fg = mg
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Different forms of energy
Name: _______________________________________
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Date: ___________
4. Replace each variable by its value and
isolate the unknown variable.
Fg = 25 kg × 9.8 N/kg
= 245 N
5. Check your solution and answer the problem
question.
The television set weighs 245 N.
18. On the surface of which planet of the solar system would you be heaviest? Explain your
answer.
On Jupiter, because the intensity of the gravitational field on the surface of this planet is the greatest
of all the planets in the solar system.
19. Look at the illustration opposite.
a) Will the mass of this explorer vehicle be the
same on Earth and Mars? Explain your
answer.
Yes, the mass of the vehicle will be the same
because the quantity of matter in an object remains
the same regardless of its location.
b) Will the weight of the explorer be the same on Earth and Mars? Explain your answer.
No, because weight depends on the intensity of the gravitational field and the gravitational field of
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Mars is weaker than that of Earth.
20. Name the type of force involved in each of the following examples.
a) pants that stick to our legs from static electricity
Electromagnetic force.
b) the force that holds together the particles in the nucleus of an atom
Strong nuclear force.
c) the friction between the gears of a watch
Electromagnetic force.
d) the string holding a helium-filled balloon
Electromagnetic force.
CHAPTER 3
Different forms of energy
8
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Date: ___________
21. Find the resultant force in each of the following situations.
a)
10 N
b)
45 N
22. Which of the following situations will have the same effect as a force of 50 N? Explain your
answer.
a) two forces of 25 N applied along the same line of action but in opposite directions
b) two forces of 25 N applied along the same line of action and in the same direction
c) two forces of 25 N applied along different lines of action but in the same direction
Situation b), because two forces applied along the same line of action and in the same direction are
added together. Their total will therefore be 50 N.
23. The motor of a boat has a propulsion force of 75 N, while the frictional force of the water
against the hull is 10 N. What is the resultant force of this system?
75 N – 10 N = 65 N
The resultant force is 65 N.
24. If you walk at a constant pace (speed), what is the resultant force of your travel?
The resultant force is zero because the motion is not altered.
25. Find the horizontal and vertical components of each of the following forces.
a)
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b)
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Different forms of energy
Name: _______________________________________
Vertical component:
Opposite side = sin 20° × 25 N
= 8.55 N
Horizontal component:
Adjacent side = cos 20° × 25 N
= 23.49 N
Class: ______________
Date: ___________
Vertical component:
Opposite side = sin 40° × 45 N
= 28.93 N
Horizontal component:
Adjacent side = cos 40° × 45 N
= 34.47 N
26. What is the effective force in each of the following situations?
The effective force is the side opposite the
25° angle.
a) The box slides down the inclined plane.
Force of gravity (Fg) = mg
= 20 kg × 9.8 N/kg
= 196 N
Opposite side = sin 25° × 196 N
= 82.83 N
The effective force is the side adjacent to the
20° angle.
b) The box slides along the ground.
Adjacent side = cos 20° × 30 N
= 28.19 N
27. A person applies a force of 200 N to the side of a piano. How much work will it take to move
the piano 5 m?
Application
1. Determine what you are looking for.
How much work will it take to move the piano 5 m?
2. Determine the different variables and their
respective values.
W=?
F// = 200 N
d=5m
3. Choose the appropriate formula.
W = F//d
4. Replace each variable by its value and
isolate the unknown variable.
W = 200 N × 5 m
W = 1000 J
5. Check your solution and answer the
problem question.
It will take 1000 J of work to move the piano.
CHAPTER 3
Different forms of energy
10
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Problem-solving steps
Name: _______________________________________
Class: ______________
Date: ___________
28. How much work does the gravitational force acting on this skier represent if the skier travels
4 m?
Calculating the effective force
The effective force is the component
parallel to the inclined plane, caused by
the force of gravity. It therefore equals
the side opposite the 15° angle.
Fg = mg
Fg = 70 kg × 9.8 N/kg
Fg = 686 N
Opposite side = sin 15° × 686 N =
177.55 N
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Problem-solving steps
Application
1. Determine what you are
looking for.
How much work is being done by the force of gravity acting on
the skier?
2. Determine the different
variables and their respective
values.
W =?
F// = 177.55 N
d =4m
3. Choose the appropriate
formula.
W = F//d
4. Replace each variable by its
value and isolate the unknown
variable.
W = 177.55 N × 4 m
= 710.2 J
5. Check your solution and
answer the problem question.
The work being done by the force of gravity acting on the skier
equals 710.2 J.
29. When work is done, energy is consumed. What happens to this energy? Explain your answer.
According to the law of conservation of energy, energy cannot be lost. The energy used during work is
transferred to the object on which the work is done.
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Different forms of energy
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Date: ___________
3 FORCES IN FLUIDS (pp. 92–98)
30. a) What is a fluid?
A fluid is a substance with the ability to spread and take the shape of the container that holds it.
b) Name four examples of fluids.
Answers will vary. Examples: water, milk, air and helium.
31. Look at the photo opposite.
a) How does water pressure act on these
objects?
The pressure is exerted perpendicularly to the
surfaces of the objects.
b) Where is the pressure greatest?
Explain your answer.
The pressure is greatest at the lowest points of
the objects in the water because pressure
increases with depth.
c) If the water is replaced by a liquid of lower density, how will the pressure change?
32. Pressure is applied to the plunger of a syringe containing 30 mL of liquid. The plunger then
exerts a pressure of 30 kPa on the liquid. If the initial pressure of the liquid was 2 kPa, what
will be the pressure of the liquid expelled at the other end of the syringe? Explain your
answer, specifying the principle of physics you used to determine the pressure.
The pressure will be 32 kPa because, according to Pascal’s principle, an increase in the pressure of an
enclosed fluid is transmitted uniformly in all directions.
33. What makes a boat float?
The fact that the buoyant force is equal to the gravitational force (the weight) of the boat.
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The pressure will be reduced because pressure also depends on the density of a liquid.
Name: _______________________________________
Class: ______________
Date: ___________
34. An object weighing 98 N is immersed in water.
a) What weight of water must be displaced so that the object can float? Explain your answer.
The weight of the displaced water must be 98 N for the buoyant force to be equal to the weight of
the object.
b) What is the volume of water displaced by the object, given that the density of water is
1 g/mL?
Problem-solving steps
Application
1. Determine what you are looking for.
What is the mass of the displaced water?
2. Determine the different variables and their
respective values.
Fg = 98 N
m =?
g = 9.8 N/kg
3. Choose the appropriate formula.
Fg = mg
4. Replace each variable by its value and
isolate the unknown variable.
98 N = m × 9.8 N/kg
m = 98 N = 10 kg
9.8 N/kg
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5. Check your solution and answer the problem The mass of the displaced water is 10 kg.
question.
The volume of water displaced by the object is 10 L.
c) The same object is immersed in a solution with a density of 0.8 g/mL.
Given that the object displaces the same volume of liquid as in b), will it float or not?
Show your calculations.
0.8 g
1 mL
=
?g
10 000 mL
The mass of the displaced liquid will be 8000 g, or 8 kg.
Problem-solving steps
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Application
13
ANSWER KEY
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Different forms of energy
Name: _______________________________________
Class: ______________
Date: ___________
1. Determine what you are looking for.
What is the weight of the displaced liquid?
2. Determine the different variables and their
respective values.
Fg = ?
m = 8 kg
g = 9.8 N/kg
3. Choose the appropriate formula.
Fg = mg
4. Replace each variable by its value and
isolate the unknown variable.
Fg = 8 kg × 9.8 N/kg
= 78.4 N
5. Check your solution and answer the problem The weight of the displaced liquid is 78.4 N.
question.
The object will sink because its weight is greater than the weight of the displaced liquid.
35. When the wind blows hard, what happens to the air pressure? Explain your answer.
According to Bernoulli’s principle, the higher the speed of a fluid, the lower its pressure. When the
wind blows hard, the air pressure drops because the air particles are moving faster.
36. Name the principle that explains each of the following situations.
a) The hull of a submarine must be very thick, from top to bottom, to resist the pressure
of the water.
Pascal’s principle.
b) To float, a submarine must empty its ballast tanks.
Archimedes’ principle.
c) Force can be amplified with a hydraulic press.
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Pascal’s principle.
d) The action of the wind makes a flag fly.
Bernoulli’s principle.
e) Warming the air in a hot-air balloon makes it rise into the air.
Archimedes’ principle.
f) Birds can fly partly because of the particular shape of their wings.
Bernoulli’s principle.
REVIEW QUESTIONS
CHAPTER 3
Different forms of energy
14
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Name: _______________________________________
Class: ______________
Date: ___________
A. To boil water, Bassima uses a microwave oven.
a) How much energy does it take to boil 250 mL of water with an initial temperature of 20°C?
Problem-solving steps
Application
1. Determine what you are looking for.
How much energy is needed to boil the water?
2. Determine the different variables and
their respective values.
Q
m
c
∆T
3. Choose the appropriate formula.
Q = mc∆T
4. Replace each variable by its value and
isolate the unknown variable.
Q = 250 g × 4.19 J/g°C × 80°C
Q = 83 800 J
5. Check your solution and answer the
problem question.
It takes 83 800 J of energy to boil the water.
=?
= 250 g
= 4.19 J/g°C
= 100°C – 20°C = 80°C
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b) Bassima calculates that to boil the water, her oven used 100 000 J of electrical energy.
What is the energy efficiency of the microwave oven?
Efficiency =
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83 800 J
= 83.8%
100 000 J
15
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Different forms of energy
Name: _______________________________________
Class: ______________
Date: ___________
B. James Prescott Joule designed many
experiments involving thermal energy. In one
of these experiments, he transformed the
mechanical energy of an object into thermal
energy, using the apparatus illustrated
opposite, known today as Joule’s apparatus.
a) How much mechanical energy do the
weights possess?
Em = Ek + Ep
Since the weights are immobile initially, their
kinetic energy equals zero. Their mechanical
energy is therefore equal to the potential energy.
Ep = mgh
Ep = 5 kg × 9.8 N/kg × 0.75 m
Ep = 36.75 J
Each of the weights has 36.75 J of mechanical energy.
b) Given an initial quantity of one litre of water at 20°C in the container, what will be the final
water temperature if the weights are lowered 20 times? The Joule apparatus is assumed to
be 100-percent efficient, and the weights move 75 cm each time they fall.
Therefore Q = 1470 J
Q
1470 J
∆T =
=
= 0.35°C
mc
1000 g × 4.19 J/g°C
Tf = ∆T + Ti = 0.35°C + 20°C = 20.35°C
C. A 10-kg chair is placed on a plane inclined at an angle of 25° to the horizontal. The plane
exerts a frictional force of 30 N on the chair. Will the chair move? Explain your answer.
Fg = mg
Fg = 10 kg × 9.8 N/kg = 98 N
Effective force = opposite side = sin 25° × 98 N = 41.41 N
The effective force is 41.41 N. Since it is greater than the force of friction, the chair will slide down the
inclined plane.
CHAPTER 3
Different forms of energy
16
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Total Em = 36.75 J × 20 × 2 = 1470 J
Since the Joule apparatus transforms mechanical energy into thermal energy,
the water absorbs 1470 J of thermal energy.
Name: _______________________________________
Class: ______________
Date: ___________
D. Fred lifts a 20-kg box to a height of 1 m.
a) How much work did Fred do to lift the box?
W = Ep = mgh = 20 kg × 9.8 N/kg × 1 m = 196 J
b) What form of energy did the box store?
Potential energy.
E. Prepare your own summary of Chapter 3 by building a concept map.
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See the Concept maps section in Guide B.
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