## Karnataka Board Class 8 Science Chapter 10 Energy and its Forms

### KSEEB Class 8 Science Chapter 10 Textual Questions & Answers

I. Four alternative are given to each of the following incomplete statement/ question. 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
d) electricity

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

Question 3.
The correct formula to find the velocity of a body with kinetic energy ‘K’ is.
a) $$\mathrm{v}=\frac{2 \mathrm{k}}{\mathrm{m}}$$
b) $$v=\sqrt{\frac{2 k}{m}}$$
c) $$\mathrm{v}=\frac{4 \mathrm{k}^{2}}{\mathrm{m}}$$
d) $$v=\frac{1}{2} k m$$
b) $$v=\sqrt{\frac{2 k}{m}}$$

Question 4.
The correct sequence of energy changes in 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
b) potential to kinetic to mechanical to electrical

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

II. Fill in the blanks with suitable words

Question 1.
Unit of power is …………
watt

Question 2.
Unit of energy is ………….
joule

Question 3.
If a candle is burnt the chemical energy is transformed into …………..
light and heat energy

Question 4.
The water stored in an overhead tank possesses ……….. energy
potential energy

Question 5.
In a cinema theater electrical energy is transformed in to ………… and ………… energy
light and sound

Question 1.
State whether the energy possed in the following is kinetic or potential.

1. compressed spring
2. stretched bow
3. moving arrow
4. water stored in a dam
5. a stone at the top of the building
6. bird resting on the branch of a tree

1. potential energy
2. potential energy
3. kinetic energy
4. potential energy
5. potential energy
6. potential energy

Question 2.
Distinguish between potential energy and kinetic energy.

1. Kinetic energy
• The energy that the body possesses due to its motion.
• It depends on the mass of the body and velocity with which it is moving kinetic energy = 1/2 mv2
2. Potential energy
• The energy which a body possesses either due to its position or due to its deformation.
• It depends on mass of the body and height to which it is raised from ground
• The potential energy = m × g × h

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

Question 4.
A ball of mass 200 grams falls from height of 5 meter ? What is its kinetic energy when it just reaches the ground ?
(g = 9.18 ms-2)
m = 200 grams = 0.2 kg
h = 5 m
u = 0
v = 7
Solution:
v2 – u2 = 2gh
v2– 02 = 2 x 9.8 x 5
v2 = 98
kinetic energy, KE = $$\frac{1}{2} m v^{2}$$
$$\frac { 1 }{ 2 }$$ × $$\frac { 200 }{ 1000 }$$ × 98 = 9.8 joule

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
4. sound energy into electrical energy
5. chemical energy into electrical energy

1. electric bulb
2. motor
3. electric heater
4. microphone
5. electric cell

Question 6.
Describe the mode of energy trans. formation in a mechanical and quartz clock.
In a mechanical clock, the spring is compressed by winding, it attains potential energy. The releasing of the spring slowly is the kinetic energy, using that the wheels of the clock turn, therefore potential energy is converted into kinetic energy. PE → KE → 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 the thermal power station?
In a thermal power station, 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.

Question 1.
What is work? Mention the factors on which the work done by a force depends on?
Work is said to be done when the point of application of a force moves.
W = F x d
The work done by the force on a body depends on two factors.

1. Magnitude of the force and
2. distance that the body moves

Question 2.
How is work done measured?
Work done by moving a body is equal to the product of force exerted on the body and the distance moved by the body in the direction of the force.
i.e, work = force x distance

Question 3.
Write the unit of work.
Work done by moving body is equal to the product of force exerted on the body and the distance moved by the body in the direction of a force. Work = Force x Distance moved in the direction of force.

Question 4.
Define Joule
Joule can be defined as when a force of on newton moves a body through a distance of one meter in its own direction.

Question 5
What is energy crisis?
If the demand for energy is more than 1 the supply then it leads to energy crisis.

Question 6.
Name the types of mechanical energy.
The two forms of mechanical energy are

1. Potential energy and
2. Kinetic energy

Question 7.
What is kinetic energy? Mention the factors that the kinetic energy of a body depends.
The energy possessed a body by virtue of its motion is called kinetic energy. KE = 1/2 mv2
Kinetic energy depends on

1. the mass of the body and
2. velocity with which it is moving

Question 8.
What is potential energy? Mention the factors that the potential energy of a body depends.
The energy which a body possesses either due to its position or due to its deformation is called potential energy.
PE = m × g × h
The potential energy of a body depends on

1. the mass of a body and
2. the height to which it is raised from the ground.

Question 9.
Give example for the potential energy.
A stretched rubber band, Mangoes in the tree, water stored in the dam, stretched bow pressed spring stretched sling of a catapult.

Question 10.
Give example for the kinetic energy.
The moving air, the moving ball, the flowing water, the moving Striker.

Question 11.
A car is moving with a uniform velocity of 15 ms-1 What is the kinetic energy of a boy of mass 40 kg sitting in the car?
m = 40 kg
v = 15 ms-1
KE = ?
Solution :
Velocity of the boy = velocity of the car kinetic energy possessed by the boy
$$=\frac{1}{2} \mathrm{mv}^{2},=\frac{1}{2} \times 40 \mathrm{kg} \times\left(15 \mathrm{ms}^{-1}\right)^{2}=4500 \mathrm{J}$$

Question 12.
If two bodies of equal masses move with a uniform velocity of‘v’ and ‘3v what will be the ratio of their kinetic energies?
Mass of first body = m
Velocity of the first body = v
mass of second body = m
velocity of second body = 3v
The ratio of the kinetic energy of the two bodies

The ratio of the kinetic energy  of the bodies = 1:9

Question 13.
A bag of wheat weighs 200 kg to what height should it be raised so that its potential energy is 9800 joule (g = 9.8 ms2)
m = 200 kg
g = 9.8 ms2
PE = 9800 J
PE = m × g × h
9800 J = 200 kg x 9.8 ms-2 x h
h = 9800
J = 200 kg x 9.8 ms-2
h = 5 m
Thus, the bag of wheat should be raised to a height of 5 m.

Question 15.
What is power?
The rate of doing work.
power = $$\frac{\text { Work }}{\text { time }}$$
The unit of power is called Watt.
1 kilowatt = 1000 w.
The unit or power is called Watt.
1kilowatt = 1000 w.

Question 16.
A body does 20 joules of work in 5 seconds. What is its power?
P = $$\frac{W}{t}$$
P = $$\frac{20}{5}$$ = 4 W