FRANK Solutions for Class 10 Physics Chapter 1.5 - Different Forms, Conservation and Transformation of Energy

Question 1

Define kinetic energy.

Solution 1

The energy possessed by a body by virtue of its motion is called kinetic energy.

Question 2

Name the type of energy possessed by a moving bullet.

Solution 2

A moving bullet possesses kinetic energy

Question 3

A body of mass 2 kg is moving with a speed of 20 ms^-1. What is its K.E.?

Solution 3

Question 4

A moving object of mass 30 kg has 60 J of kinetic energy. What is its speed?

Solution 4

Question 5

What type of energy is possessed by a flowing water?

Solution 5

Flowing water possesses kinetic energy.

Question 6

If the speed of a particle is increased four times, how will its kinetic energy be affected?

Solution 6

Question 7

A bus and a car have the same K.E. which of the two should be moving faster? Explain.

Solution 7

The car should be moving faster because the mass of the car is less than that of the bus.

Question 8

A body is thrown vertically upwards. Its velocity keeps on changing. What happens to its K.E. when does its velocity become zero?

Solution 8

Its kinetic energy changes with the change in velocity.
Velocity becomes zero at the highest point.

Question 9

What change should be effected in the velocity of a body to maintain the same K.E., if its mass is increased four times?

Solution 9

Question 10

The K.E. of a body is 5 J. What will be its K.E. when its speed is doubled?

Solution 10

Question 11

Name the parameters that can change the K.E.

Solution 11

The parameters that can change the kinetic energy are:
(i) Mass
(ii) Speed

Question 12

Give two examples of kinetic energy.

Solution 12

Examples of kinetic energy:
(i) Air in motion has kinetic energy.
(ii) A swinging pendulum

Question 13

Give an example of a body possessing no K.E.

Solution 13

A ball at lying at rest on the floor possesses zero kinetic energy.

Question 14

Define potential energy.

Solution 14

The energy possessed by a body by virtue of its position, shape or change of configuration is called potential energy.

Question 15

What are the factors on which P.E. of a body depends?

Solution 15

Potential energy of a body depends upon:
(i) Mass of the body
(ii) Acceleration due to gravity
(iii) Height of the body

Question 16

What is the amount of energy spent in lifting 1 kg through 1 m? Take g = 10 ms^-2.

Solution 16

Question 17

Give two examples of P.E.

Solution 17

Examples of potential energy:
(i) Water stored at a height in a reservoir.
(ii) A stretched spring.

Question 18

What is the P.E. of a body lying on the surface of the earth?

Solution 18

P.E of a body lying on a floor is zero.

Question 19

What is the amount of energy spent by the heart in pumping blood through the body?

Solution 19

The energy spent by the heart in pumping blood through the body is 1 J per beat.

Question 20

Name the type of energy possessed by a body due to a change in configuration.

Solution 20

Potential energy

Question 21

How is energy stored in a clock?

Solution 21

The work done in winding a clock spring is stored as P.E. in the spring. This P.E. is then used to run the hands of the clock.

Question 22

What is the P.E. of a body of mass M at a height H above the earth's surface?

Solution 22

P.E. of a body of mass M and at a height H above the earth's surface is:
P.E. = MgH ; here, g = acceleration due to gravity.

Question 23

Write the SI units of energy.

Solution 23

SI unit of energy is 'joule'.

Question 24

Is P.E. a vector or a scalar quantity?

Solution 24

P.E. is a scalar quantity.

Question 25

Name the type of energy possessed by a
(i) stretched catapult        (ii) hot iron
(iii) wound up clock

Solution 25

(i) Potential energy
(ii) Heat energy
(iii) Potential energy

Question 26

An object is dropped from a height H. when is its
(a)    P.E. maximum,
(b)    K.E. maximum,
(c)    P.E. = K.E.?

Solution 26

(i) At the height H because the height is maximum.
(ii) At the ground level because the velocity is maximum.
(iii) At half distance of the total path i.e. at height H/2, the P.E. is equal to the K.E.

Question 27

A cricket ball is thrown up from the earth's surface. What happens to its P.E.
(a)    during the motion
(b)    at the highest point?

Solution 27

(a) As the height above the ground increases, the potential energy also increases.
(b) At the highest point, the height of the cricket ball is maximum and hence the potential energy is also maximum.

Question 28

Name the physical quantity which is equal to the energy of a body.

Solution 28

Work

Question 29

Name the physical quantity which is associated with the work done by a body.

Solution 29

'Energy' is the body's ability to do work.

Question 30

Is kinetic energy a scalar or a vector physical quantity?

Solution 30

Energy is a scalar quantity.

Question 31

If the speed of a body is doubled, what happens to its kinetic energy?

Solution 31

Question 32

What are the physical parameters on which the kinetic energy of a body depends?

Solution 32

Kinetic energy of a body depends upon:
(i) Mass of the body
(ii) Speed of the body

Question 33

Can a body possess zero kinetic energy?

Solution 33

Yes, if the body is not in motion; it has zero kinetic energy

Chapter 1.5 - Different Forms, Conservation and Transformation of Energy Exercise 54

Question 1

What is the difference between K.E. and P.E.?

Solution 1

P.E. is the energy possessed by a body by virtue of its position, shape or configuration but K.E. is the energy possessed by a body by virtue of its velocity or motion.
E.g. A ball kept on a cliff possesses P.E. but as soon as it is kicked it possesses K.E.

Question 2

What is meant by the transformation of energy?

Solution 2

Whenever one form of energy dissipates or disappears, another form of equivalent amount of energy is produced; this is referred to as transformation of energy.
E.g. when a particular switch is pressed electric lamps light up owing to the heat produced in the filament. This is the transformation of electrical energy to heat and light energy.

Question 3

Does the total energy of a body always remain constant?

Solution 3

No, total energy of a body does not remain constant but the total energy of a closed system remains constant e.g. universe.

Question 4

Is energy a scalar or a vector physical quantity?

Solution 4

Energy is a scalar quantity.

Question 5

Can we destroy every energy associated with a body?

Solution 5

No, we cannot destroy energy associated with a body.

Question 6

Define energy of a body.

Solution 6

Energy is the capacity or ability of a body to do work or energy is stored work.

Question 7

State the law of conservation of energy.

Solution 7

The law of conservation of energy states that energy cannot be created or destroyed; the sum total of energy in a closed system remains unchanged. Energy only changes from one form to another.

Question 8

A dry cell converts one form of energy into another. Name the two forms.

Solution 8

A dry cell converts chemical energy into electrical energy.

Question 9

Name the device that converts electrical energy into mechanical energy.

Solution 9

A D.C. motor converts electrical energy into mechanical energy.

Question 10

Name the device that converts mechanical energy into electrical energy.

Solution 10

A dynamo converts mechanical energy into electrical energy.

Question 11

Name four different forms of energy.

Solution 11

Four different forms of energy:
(i) Solar energy
(ii) Mechanical energy
(iii) Wind energy
(iv) Nuclear energy

Question 12

What kind of energy transformation takes place at a thermal power station?

Solution 12

At a thermal power station, nuclear energy is converted into electrical energy.

Question 13

Name the energy changes for each of the following cases:
(i) electric ball         (ii) bicycle brakes
(iii) pendulum            (iv) human body      
(v) dynamo

Solution 13

(i)     Electrical energy to sound energy
(ii)     Mechanical energy into heat energy.
(iii)    Potential energy into kinetic energy and vice-versa.
(iv)    Chemical energy obtained from food is converted into mechanical energy and heat energy in muscles.
(v)     A dynamo converts mechanical energy into electrical energy.

Question 14

What is meant by power?

Solution 14

The rate of doing work is called power.

Question 15

Write the SI units of power.

Solution 15

'Watt' is the SI unit of power.

Question 16

Define one horse power.

Solution 16

Horse power is the unit of power. The horsepower used for electrical machines is defined as exactly 746 watt.
Classically, a horse exerting 1 H.P. can raise 330 pounds of coal 100 feet in a minutes, or 33 pounds of coal 1,000 feet in one minute, or, 1,000 pounds 33 feet in one minute.

Question 17

Define the unit 'watt'. How is it related to horse power?

Solution 17

If 1 joule of work is done in 1 second, the power is said to be 1 watt.
1 H.P. = 746 watt

Question 18

A body does 20 J of work in 10 s. What is its power?

Solution 18

Question 19

Name the physical quantity associated with the 'rate of doing work'.

Solution 19

Power is the physical quantity associated with the 'rate of doing work'.

Question 20

An electric motor drives a machine which lifts a mass of 4 kg through a height of 10 m in 5 s at a constant speed. Assuming g = 10 ms^-2, calculate

(i) the amount of work done,    (ii) the power of the machine.

Solution 20

Question 21

Name the practical unit of power.

Solution 21

Practical or commercial unit of power is kilowatt-hour.

Question 22

In what form is energy stored in a wrist watch?

Solution 22

When we wind a watch, the configuration of its spring is changed. The energy stored in the spring is obviously potential in nature (elastic potential to be more accurate).

Question 23

A log of wood cut by a saw becomes hot. From where does this heat energy come?

Solution 23

This heat energy comes from the mechanical energy.

Question 24

Our hands become warm when we rub them against each other. Why?

Solution 24

When we rub our hands, mechanical energy is converted into heat energy.

Question 25

The head of a nail becomes warm when it is hammered into a plank of wood. Explain the series of energy transformation taking place in the process.

Solution 25

When the head of a nail is struck with a hammer, the mechanical energy of the hammer pushes the nail into the plank of wood and in this process a part of energy is converted into heat energy.

Question 26

A 100 W electric lamp emits energy in the form of light at the rate 10 J per second. What percentage of electric energy does the lamp transform into light energy?

Solution 26

Question 27

A horse exerts a pull on a cart of 300 N so that the horse-cart system moves with a uniform speed 18 km/h on a level road. Calculate the power developed by the horse in watt and also find its equivalent in horse power.

Solution 27

Question 28

If an electric bulb of 100 watt is lighted for 2 hours, how much electric energy would be consumed?

Solution 28

Question 29

A woman pulls a bucket of water of total mass 5 kg from a well which is 10 s. calculate the power used by her.

Solution 29