KSEEB Solutions for Class 8 Science Chapter 10 Energy and its Forms

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Karnataka State Syllabus Class 8 Science Chapter 10 Energy and its Forms

KSEEB Class 8 Science Energy and its Forms Textbook Exercise Questions and Answers

I. Four alternatives are given to each of the following incomplete statements/questions choose the right answer.

Question 1.
The type of energy that can be easily converted into other forms is
(a) sound
(b) light
(c) heat
(d) electricity
Answer:
(d) electricity

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Question 2.
Kinetic energy is present in the following is
(a) water stored in a dam
(b) stretched rubber band
(c) water released from a dam
(d) compressed spring
Answer:
(c) water released from a dam

Question 3.
The correct formula to find the velocity V of a body with Kinetic energy ‘K’ is
(a) v = 2k/m
(b) v = \(\sqrt{2 \mathrm{k} / \mathrm{m}}\)
(c) v = 4k2/m
(d) v = 1/2 km
Answer:
(b) v = \(\sqrt{2 \mathrm{k} / \mathrm{m}}\)

Question 4.
The correct sequence of energy changes in a hydroelectric power station is
(a) Kinetic to potential, to mechanical to electrical
(b) Potential to Kinetic to mechanical to electrical
(c) Potential to electrical to mechanical
(d) Potential to electrical to kinetic to mechanical.
Answer:
(b) Potential to Kinetic to mechanical to electrical

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Question 5.
Which object with the mass indicated has higher potential energy?
a) mass = 10 kg g= 9.8 ms-2 h = 10m
b) mass = 5 kg g = 9. 8ms-2 h = 12m
c) mass = 8 kg g = 9.8 ms-2 h = 100m
d) mass = 6 kg g = 9.8 ms-2 h = 20m
Answer:
c) mass = 8 kg g = 9.8 ms-2 h = 100m

II. Fill in the blanks with suitable words:

Question:
1. Unit of power is ______________.
2. Unit of energy is ______________.
3. If a candle is burnt, the chemical energy is transformed into ______________.
4. The water stored in an overhead tank possesses ______________ energy.
5. In a cinema theatre electrical energy is transformed into ______________ and ______________ energy.
Answer:
I. Watt,
2. Joule,
3. light and heat energy,
4. potential energy,
5. light and sound

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III. Answer the following:

Question 1.
State whether the energy possessed in the following is kinetic or potential;
(a) compressed spring
(b) stretched bow
(c) moving arrow
(d) water stored in a dam
(e) a stone at the top of the building
(f) bird resting on the branch of a tree
Answer:
a. potential energy
b. potential energy
c. kinetic energy
d. potential energy
e. potential energy
f. potential energy

Question 2.
Distinguish between potential energy and kinetic energy.
Answer:
Potential Energy

  • The energy possessed by a body by virtue of its position.
  • P. E depends on the mass of the body and height to which it is raised from the ground.
  • P.E = mgh

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Kinetic Energy

  1. The energy possessed by a body by virtue of its motion
  2. K.E depends on the mass of the body and velocity with which it is moving
  3. KE = \(\frac{1}{2}\) mv-2

Question 3.
A bus and a car are moving at the same speed. Which of the two has greater kinetic energy?
Answer:
The bus has greater kinetic energy since it has got greater mass than the car, even though they, are moving at the same speed.

Question 4.
A ball of mass 200 grams falls Trom height of 5 metres. What is its kinetic energy when it just reaches the ground?
Answer:
mass = 200 grams = 0.2 kg (g = 9.8 ms-2)
h = 5 metres u = 0 V = ?
V2 – u2 = 2 gh
v2 – 02 = 2 x 9.8 x 5 = 98
\(\mathrm{KE}=\frac{1}{2} \mathrm{mv}^{-2}=\frac{1}{2} \times \frac{200}{1000} \times 98=9.8 \mathrm{joule}\)
or
PE = mgh
= 2 x 9.8 x 5
= 9.8 joules
Since PE is converted into KE
PE = KE = 9.8 joules

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Question 5.
There are a number of devices in common use that change energy from one form to another. Name some devices that change.
1. electrical energy into light energy,
2. electrical energy into mechanical energy,
3. electrical energy into heat energy,
4. sound energy into electrical energy,
5. chemical energy into electrical energy.
Answer:
1. electric bulb
2. motor
3. electric heater/electric iron box/electric fuse
4. microphone
5. Electric cell

Question 6.
Describe the mode of energy transformation in a mechanical and quartz clock.
Answer:
In a mechanical clock, the spring is compressed by winding, and it attains potential energy. The releasing of the spring slowly is the kinetic energy, using which the wheels of the clock turn which is mechanical energy. Therefore potential energy is converted into kinetic energy, potential energy → kinetic energy → mechanical energy.

In the quartz clock, the electric cell gives the electrical energy and it is converted into mechanical energy by which the wheels of the clock turns. Therefore the energy transformation is chemical energy → electrical energy → mechanical energy.

Question 7.
What kind of energy transformation takes place at a thermal power station?
Answer:
Coal is used to generate heat, and water is boiled. The resulting steam is used to drive the turbine which is connected to a generator. So the energy transformation at the thermal power station can be written as. Chemical energy → heat energy → mechanical energy → electrical energy

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KSEEB Class 8 Science Energy and its Forms Additional Questions and Answers

Question 1.
What is work?
Answer:
Work is said to be done when the point of application of a force moves.

Question 2.
Mention the two factors on which the work is done by a force depends.
Answer:
The work done by a force on a body depends on two factors, the magnitude of the force and the distance that the body moves.

Question 3.
How is work done measured?
Answer:
Unit of work is newton meter is written as Nm equal to one ‘Joule’. Unit of work is called joule.

Question 4.
What is a joule?
Answer:
Joule can be defined as the work done when a force of one newton moves a body through a distance of one metre in its own direction.

Question 5.
Name the types of mechanical energy.
Answer:
The two forms of mechanical energy are potential energy and kinetic energy.

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Question 6.
Mention the factors on which the kinetic energy of a body depends.
Answer:
The kinetic energy of a body depends upon the mass of the body and the velocity with which it is moving.

Question 7.
Mention the factors on which the potential energy of a body depends.
Answer:
The potential energy of a body depends upon the mass of a body and the height to which it is raised from the ground.

Question 8.
What is meant by the transformation of energy?
Answer:
The change of energy from one form to another is known as the transformation of energy.

Question 9.
State the Law of conservation of energy.
Answer:
Energy can neither be created nor destroyed. It can be converted from one form to another. This is known as the Law of conservation of energy.

Question 10.
What is power?
Answer:
The rate of consumption of energy is known as power.

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II. Fill in the blanks:

Question:

  1. If the demand for energy is more than the supply then it leads to ______________.
  2. All the moving bodies possess ______________.
  3. The energy that the body possesses due to its motion is called ______________.
  4. Higher the velocity, the higher the energy ______________.
  5. Higher the mass of the body, the higher the ______________ energy.
  6. The energy which a body possesses due to its position is called ______________.
  7. The energy possessed by a body due to its deformation is called ______________.
  8. Higher the body raised from the ground, the higher the ______________ energy.
  9. When the rate of consumption is higher the ______________ unit is used.
  10. The ultimate source of energy is ______________.

Answer:

  1. energy crisis
  2. Kinetic energy
  3. kinetic energy
  4. kinetic
  5. Kinetic and potential energies
  6. potential
  7. potential
  8. potential
  9. Kilowatt
  10. Sun.

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III. Match the following:
A – B
1) Work – a) m g h
2) Power – b) mass x velocity
3) Kinetic energy – C) u + at
4) Potential energy – d) wit
5) Momentum – e) sp x t
6) Acceleration – f)ma
7) Distance traveled – g) Force x distance
8) Velocity – h) v-u/t
9) Force – i) \(\frac{1}{2}\) mv2
Answer:
1. g,
2. d,
3. i,
4. a,
5. b,
6. h,
7. e,
8. c,
9. f.

IV. Write the S.l units for the following:

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Question:

  1. Distance traveled
  2. Displacement
  3. Speed
  4. Velocity
  5. Acceleration
  6. Force
  7. Momentum
  8. Work
  9. Power
  10. Acceleration due to gravity

Answer:

  1. metre,
  2. metre,
  3. ms-1
  4. ms-1,
  5. ms-2,
  6. kg ms-2 or N,
  7. Kg ms-1,
  8. Nm or joule.
  9. Watt,
  10. ms-2

V. Choose the correct answer:

Question 1.
In which of the following cases is work being done?
a) A man pushing a wall
b) A boy climbing up a staircase
c) A coolie standing with a load of 10 kg on his head.
d) A boy trying to lift a huge rock which is fixed.
Answer:
b) A boy climbing up a staircase

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Question 2.
One joule work is said to be done when
a) A force of 1 N displaces a body by 1 cm
b) A force of 10 N displaces a body by 1 m
c) A force of 10 N displaces a body by 1 Km
d) A force of 1 N displaces a body by 1 cm.
Answer:
a) A force of 1 N displaces a body by 1 cm

Question 3.
Which one of the following statements is true?
a) Work and energy have different units.
b) The potential energy of a spring increases as it is extended.
c) When a body falls, its kinetic energy remains constant.
d) The potential energy of an object on the ground is zero.
Answer:
d) The potential energy of an object on the ground is zero.

Question 4.
A particle of mass 100 gm moves at a speed of 1 m/s? Its kinetic energy is
(a) 5 J
(b) 0.5 J
(c) 0.05 J
(d) 50 J
Answer:
(c) 0.05 J

Question 5.
The kinetic energy of a body depends
(a) on its mass
(b) on its velocity
(c) on its mass and velocity
(d) neither on its mass and velocity
Answer:
(c) on its mass and velocity

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Question 6.
A force of a given magnitude acts on a body. The acceleration of the body is proportional to its
(a) mass
(b) volume
(c) density
(d) shape
Answer:
(a) mass

Question 7.
The momentum of a body of a given mass is proportional to
(a) volume
(b) velocity
(c) volume and velocity
(d) weight
Answer:
(b) velocity

Question 8.
When a log of wood rolls down on an inclined plane it has
(a) kinetic energy
(b) potential energy
(c) both potential and kinetic energy
(d) Neither potential nor kinetic energy
Answer:
(c) both potential and kinetic energy

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Question 9.
The work is said to be done by a force when the body.
(a) moves perpendicular to the direction f of the force applied.
(b) moves opposite to the direction of the force applied.
(c) moves along the direction of the force applied.
(d) does not move
Answer:
(c) moves along the direction of the force applied.

Question 10.
Raju does 500 J of work in 10 minutes and Vikram does 800J of work in 20 1 minute. If the power of Raju be X I and Vikram be Y then.
(a) X = Y
(b) X > Y
(c) X < Y
(d) X < Y
Answer:
(b) X > Y

Question 11.
A ball is thrown upwards from a point A and stops at a point B. Which statement is true in this case?
(a) K E at A = K E at B
(b) K E at A = P E at B
(c) P E at A = P E at B
(d) PE at B = K E at B
Answer:
(b) K E at A = P E at B

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Question 12.
When a force of 1 N acts on a mass of 1 kg, is free to move, then the object moves with a
(a) speed of 1 m/sec
(b) speed of 1 km/sec
(c) acceleration of 10 m/sec2
(d) acceleration of 1 m/sec2
Answer:
(d) acceleration of 1 m/sec2

Question 13.
Two bodies of equal masses are moving with uniform velocities V and 2V. The ration of their kinetic energy is
(a) 1:2
(b) 2 : 1
(c) 1 : 4
(d) 4 : 1
Answer:
(c) 1 : 4

Question 14.
When a net force acts on an object the object will be accelerated in the direction of the force with an acceleration proportional to
(a) the force on the object
(b) mass of the object
(c) the velocity of the object
(d) the inertia of the object
Answer:
(b) mass of the object

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