DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

SCIENCE FORM 3
2020
(NOTES, PBD, EXERCISE)
NAME:
CLASS:
TEACHER: PN. JULIA BINTI AHMAD

CHAPTER : 7 ENERGY AND POWER

CONTENT CONTENT DATE TEACHER’

STANDARD S SIGN
7.1 Work, energy and power

7 7.2 Potential Energy and Kinetic

ENERGY AND POWER Energy
7.3 Principle of Conservation of
Energy

NOTES

7.1 WORK, ENERGY AND POWER

Work

1. Work, W, is defined is defined as the product of __force, F,____ and ___displacement, s_______, in the
direction of the force, that is __W= Fs______.
2. The S.I. unit for work is __joule (J)______

1
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
 1 joule (J) of work is done when a ___force of 1 newton (N)___ is used to move an object over a
___1 metre (m)___ in the direction of the force, that is ___1 J = 1 Nm____
3. ___movement of force___________________ and __energy__________are two physical quantities other
than work which are measured in units of _newton metre_______________________(Nm). Larger units
such as __kilojoule (kJ)___________ and __megajoule(MJ)____________________ are also used in the
measurement of work.

ACTIVITY A

 Force = 20N
 Direction of force= vertivcal
 Displacement in the direction of the force= 1m
 Work done?
W=Fs
= 20N x 1m
= 20 J

ACTIVITY B
 Force = 10N
 Direction of force=horizontal
 Displacement in the direction of the force=5m
 Work done?
W=Fs
= 10N x 5m
= 50J

ACTIVITY C
 Force = 2N
 Direction of force= Horizontal
 Displacement in the direction of the force=0.3
m
 Work done?
W=Fs
= 2N x 0.3m
= 0.6 J

Examples of Calculation of Work in Daily Activities

Calculation of work done

Example Solution
1.
W=Fs
= (400 + 100) N x 3m
2
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
Figure below shows a student weighing 400 N carrying a load = 500 N x 3m
of 100 N while climbing a flight of stairs of a vertical = 1500J

height of 3 m. Calculate the work done

2. Figure below shows Ali lifting a box of mass 10 kg from Weight of box = 10 x 10 N
the floor to the top of a cupboard. How much work is done = 100 N
W=Fs
by Ali? (Assume gravitational force acting on an object of
= 100N x 2m
mass 1 kg = 10 N) = 200J

3. A labourer pulled a bucket of cement weighing 300 N W=Fs

from the ground to the first floor of a building using a = 300N x 10m
= 3000J
pulley system. The first floor is 10 m from the ground.
What is the work done by the labourer?

Energy and Power

1. Energy is defined as __the ability to do work

2. The S.I. unit for energy is ___joule (J)_______________________________
 When a _force of 1N_________ is used to move an object over a _distance of 1m___ in the
direction of the force, _1J of energy_______ is used.
3. Power, P, is defined as __the rate of doing work, W___________, that is:

3
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

4. The S.I. unit for power is __watt (w)________________.

 When __1 joule (J) of work_____s done in __1 second (s)___, power of __1 watt (w)____ is
used,
that is _1W= 1Js-1______________________________

Examples of Calculation of Power in Daily Activities

ACTIVITY D
A monkey weighing 50 N climbed a height of 3 m up a tree  Force = 50N
in 20 s.
 Direction of force=Vertical
 Displacement in the direction of the force=3m
 Work done=
W = Fs
= 50N x 3m
= 150 J

 Time taken= 20s

 Power?
P = W/T
= 150J / 20 s
= 7.5 W

ACTIVITY E
 Force = 30N
Aizul pulled a box up a smooth ramp from A to B with a  Direction of force= vertical
force of 30 N over a distance of 2 m (in the direction of the
 Displacement in the direction of the force= 2m
force) in 5 s.
 Work done?=
W = Fs
= 30N x 2m

4
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
= 60 J

 Time taken= 5s
 Power?
Power = work done / time taken
= 60J / 5 s
= 12W

ACTIVITY G
 Force = 150N
A 150 N weight is lifted to a height of 1 m in 0.5 s.
 Direction of force= vertical
 Displacement in the direction of the force=1m
 Work done?=
Work = Fs
= 150N x 1m
= 150 J

 Time taken= 0.5 s

 Power?

Power = work done / time taken

= 150 J / 0.5 s
= 300 w

CONTENT STANDARD: 7.15 WORK, ENERGY AND POWER

pbd CONTENT STANDARD .1 RESPIRATORY SYSTEM
PBD
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

1. What are the unit and symbol for work?

PL1
Unit: ___joule______________ Symbol:______J__________

PL1
2. Mark ( ✓ ) the factors that affect work done.
Time / Force / Displacement

3. What are the unit and the symbol for power? PL1

Unit: ___watt__________________ Symbol:________W______________

4. Mark ( ✓ ) the factors that affect the power generated. PL1

/ Time / Force Mass / Displacement

5. Mark ( ✓ ) in the boxes below the activities that involve work done in everyday life.
Pushing Walking Washing clothes Sitting on the
a concrete wall floor

6. Solve the following questions by using these formula: PL3/KBA

T

(a) ,The diagram on the right shows a student lifting a weight, 0.5 m vertically from the floor. If the force
recorded on the spring balance is 5 N, calculate the work done by the student.
Work done = force x displacement
= 5N x 0.5m
= 2.5 J

P3/KBATA boy pushed a 20 kg box over a distance of 2 m. Calculate the work done. [1kg = 10 N]
6
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

1kg = 10N
= 20kg x 10N
= 200N
Work done = force x displacement
= 200N x 2m
= 400J

(b) A worker had done 150 J of work in 5 s. Calculate the power he generated.

Power = work done / time taken

= 150J / 5s
= 30 W

(c) Syed which weighs 70 kg takes 8 seconds to run up a flight of stairs which has vertical height of 15 m.
what is Syed’s power?(1kg=10N)
1kg = 10N
= 70kg x 10N
= 700N
Work done = force x displacement
= 700N x 15m
= 10 500J

Power = work done / time taken

= 10 500J / 8 seconds
= 1312.5W

(d) A woman weighs 720 N pushes a trolley loaded with 340 N over a distance of 55 m. if her power
output is 100 W, how much time does she take?
Work done = force x displacement
= 340N x 55m
= 18700 J
Power = work done / time taken
100w = 18700J/x
= 187s
= 3.12m

7
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
NOTES
7.2 POTENTIAL ENERGY AND KINETIC ENERGY
Gravitational Potential Energy
1. Gravitational potential energy is ___ the work done to lift an object to a height, h, from the Earth's
surface._____

Relationship between Work and Gravitational Potential Energy

Figure shows an object of mass, m, being lifted vertically to a height, h, from

Earth’s surface.
 Work done = Force × displacement in direction of force = Weight ×
height lifted = (m × g) × h = mgh
 Since there is ____ other form of energy produced, all _work
done___________ on the object will be converted to ___gravitational
potential energy._____ _.
Gravitational potential energy = work done = __mgh____

Example of numerical problem

Example Solution
1. Photograph below shows a lift at KLCC mall. a) work done = force x displacement
The lift can carry a load of mass 1 500 kg to a 1kg = 10N
height of 30 m. = 1500kg x 10N
a) How much work = 15 000J
is done by this lift? Work done = 15 000 J x 30 m
(b) What is the = 450 000J
gravitational b) gravitational potential energy = mgh
potential energy of mgh
this lift at a height of 1500 x 10ms-1 x 30m
30 m? = 450 000J
(c) What is the c) Work done by the lift = Gravitational potential energy
relationship between of the lift
work done by the lift d) power = work done / time taken
and gravitational 0.5m x 60s = 30s 1kW = 1000w
potential energy of 450 000J/30s = 15000w
the lift? 15000w /1000 = 15kW
(d) What is the power of the lift in kW if the time
8
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
taken to lift a load of mass 1 500 kg to a height of
30 m is 0.5 minutes?
2. Figure below shows an eagle of mass 2 kg Gravitational energy = mgh
perches on the Petronas Twin Towers. If the Mass = 2kg
gravitational potential energy of the eagle is 9 Height = ?
000 J, what is the height, h of the eagle from the GE= 9000J (gravitational energy)
Earth’s surface?
Mass = 1kg = 10N
=2kg x 10 N
= 20N
Mgh = 20N x 10ms-2x h
9000J = 20(h)
h = 9000J / 20
h = 450m
3. Figure below shows a sphere of mass 3 kg being Mgh
pushed along a smooth inclined plane. What is Mass = 3kg = 30N (1kg =10N)
the gravitational potential energy of the sphere mgh = 3kg x 10ms-2 x 0.5m
when it reaches point Y? = 15J

Elastic Potential Energy

1. A spring that is ___compressed___ or _ stretched______possesses ___elastic potential energy_______
2. Elastic potential energy is ___the work done to compress or stretch an elastic material over a displacement of
x from the position of equilibrium_____

Relationship between Work and Elastic Potential Energy

9
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

Example of numerical problem

Example Solution
1. The original length of spring S is 20 cm. When the Distance of compression , x
final force exerted on spring S is 20 N, its new = original length = 20 cm
length becomes 12 cm. Calculate the elastic = new length = 12cm
potential energy possessed by the compressed Original length – new length
spring S. = 20cm – 12cm
= 8 cm converted to m (1m = 100cm)
= 0.08 m

½ Fx
½ x 20N x 8cm

2. The original length of spring X is 1.0 m. When

the final force exerted on spring X is 150 N, the
new length becomes 1.5 m. Calculate the elastic
potential energy possessed by the stretched
spring X.

3. A force of 200 N is used to stretch a bowstring 20

cm in the direction of force as shown in Figure 2.

10
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
Calculate the elastic potential energy possessed
by the stretched bowstring.

Kinetic Energy
1. Kinetic energy is the energy
________________________________________________________________________

Example Solution
1. When a train of mass 500 000 kilogram
moves with a velocity of 360 km h–1,
how much kinetic energy is possessed by
the train?

2. A ball bearing of mass 0.2 kg possesses

kinetic energy of 3.6 J. What is the
velocity, v of the ball bearing

3. Calculate the kinetic energy of an

11
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
electron of mass 9 × 10–31 kg and
velocity 4 × 106 m s–1.

CONTENT STANDARD: 7.2 POTENTIAL ENERGY AND KINETIC ENERGY

pbd
CONTENT STANDARD .1 RESPIRATORY SYSTEM
PBD
CONTENT STANDARD : 2.1 RESPIRATORY SYSTEM

1. Gravitational potential energy is the work done to lift an object to a height, h from the Earth’s surface.

Gravitational potential energy = Work done = Force (N) × Displacement (m) = mgh
.
Solve the numerical problem about the gravitational potential energy by using the formula above.
3/KBAT PL3/KBA
T
The photo on the right shows a lift in a shopping centre that carried a 500 kg load to
a height of 20 m in 20 s. (g is estimated as 10 m s–2)
(a) What is the word done by the lift?

(b) What is the gravitational potential energy of the lift at the height of 20 m?

12
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

(c) Calculate the power of the lift.

2. Elastic potential energy is the work done to compress or stretch a elastic material with displacement x from
the equilibrium position.

Solve the numerical problem about the elastic potential energy by using the formula above. TP3/KBAT
PL3/KBA
T

The diagram on the right shows a compressed spring. The original length of the spring is 15 cm. The length
of
the spring becomes 10 cm when a force of 20 N is applied.

(a) What is the compression distance, x of the spring?

(b) Calculate the elastic potential energy possessed by the compressed spring.

13
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

3. Kinetic energy is the energy possessed by a moving object

Solve the numerical problem about the kinetic

PL3/KBA
T
(a) The photo on the right shows an aeroplane flying in the sky. The plane has a mass
of 80 000 kg and flew at a speed of 900 km h–1. Calculate the kinetic energy of the aeroplane.

(b) The photo on the right shows a bullet train moving at a velocity of 360 kmh– 1. If the bullet train has a
mass of 600 000 kg, calculate the kinetic energy possessed by the train.

14
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

NOTES

7.3 PRINCIPLE OF CONSERVATION OF ENERGY

Principle of Conservation of Energy

1. The Principle of Conservation of Energy states that ____________________________________but can

only be ___________________from one form to another.
2. Oscillating systems such as the oscillation of a simple pendulum and the oscillation of a loaded spring
always experience _____________________ in the forms of energy between
__________________________ or _______________________________
and____________________________________.

Oscillating Systems Obey the Principle of Conservation of Energy

1. Complete the table below

Condition of pendulum Transformation in the forms of energy for the bob between gravitational potential
bob energy (gravitational P.E.) and kinetic energy (K.E.)
At position X Gravitational P.E =
K.E =
 Gravitational P.E of bob
__________________
15
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
K.E of bob
_______________________________
At position Y Gravitational P.E =
K.E =
 Gravitational P.E of bob
___________________
K.E of bob
________________________________
At position Z Gravitational P.E =
K.E =
 Gravitational P.E of bob
___________________
K.E of bob
________________________________
At position Y Gravitational P.E =
K.E =
 Gravitational P.E of bob
___________________
K.E of bob
________________________________
At position X Gravitational P.E =
K.E =

2. Complete the table below

Condition of loaded Transformation in the forms of energy for the load between elastic potential
spring energy (elastic P.E.) and kinetic energy (K.E.
At position X Elastic P.E =
K.E =
 Elastic P.E __________________
K.E ________________________
At position Y Elastic P.E =
K.E =
16
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
 Elastic P.E ___________________
K.E __________________________
At position Z Elastic P.E =
K.E =
 Elastic P.E ___________________
K.E __________________________
At position Y Elastic P.E =
K.E =
 Elastic P.E ___________________
K.E ___________________________
At position X Elastic P.E =
K.E =

Transformation of Kinetic Energy and Potential Energy in a Closed System

In a __________________system, the _____________________________ between potential energy and kinetic

energy ___________ the Principle of Conservation of Energy. Therefore, the total potential energy and kinetic
energy in a closed oscillation system is ____________________.

Example of numerical
Example Solution
1. Figure below shows a toy pistol. The length of the
spring in the toy pistol is 300 mm. If a force of 5 N
is used to compress the spring until its length
becomes 50 mm, calculate the maximum speed of
the plastic ball of mass 50 g when it is fired from
the pistol. State an assumption that is made in
solving this problem.

2. The diagram below shows a body X of mass 5 kg

17
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
placed on a compressed spring. When the spring
is released, the body X is pushed up as high as 20
cm.

(a) How much elastic potential energy stored in

the compressed spring?
(b) What is the maximum kinetic energy of body
that is pushed up?

pbd CONTENT STANDARD: 7.3 PRINCIPLE OF CONSERVATION OF ENERGY

PBD CONTENT STANDARD : 2.1 RESPIRATORY SYSTEM

1. Answer the questions below. PL1

Energy cannot be created or destroyed but can only change its form.

Based on the statement above, tick ( ✓ ) the principle.

( ) Hydraulic principle ( ) Principle of conservation of energy ( ) Bernouli’s principle

2. Read the statement below.

Swing systems such as the swing of simple pendulum and swing of spring are always undergone
transformation of energy whether gravitational or elastic potential energy and kinetic energy in
accordancewith the principle of conservation of energy.
18
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER

Based on the statement above, write ‘GPE’ or ‘’KE’ for the transformation of the energy form for the pendulum.

PL2
Gravitational potential energy – GPE Kinetic energy – KE

3. Write ‘EPE’ or ‘’KE’ for the transformation of the energy form for the swing of spring. Give explanations.
PL2

19
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
Elastic potential energy - EPE Kinetic energy – KE

PL3/KBA
T

4. Solve this numerical problem related to the conservation of energy.

20
DATE: ______________ DAY: ____________________ CHAPTER 7: ENERGY AND POWER
(a) A 10. kg ball is thrown into the air. It is going 3.0 m/s when thrown. How much potential energy will it
have at the top?

(b) A 4.00 kg ball is on a 5.00 m ledge. If it is pushed off the ledge, how much kinetic energy will it have
just before hitting the ground?

(c) A 25 kg ball is thrown into the air. When thrown it is going 10. m/s. Calculate how high it travels.

(d) A 3.0 kg rock sits on a 0.80 meter ledge. If it is pushed off, how fast will it be going at the bottom?

21