Living Science Physics Class 7 ICSE Solutions Chapter 3 Energy

ICSE Living Science Physics for Class 7 Solutions Chapter 3 Energy

Think And Answer (Page-37)

All stored energy is potential energy. Do you agree?
Answer:
No, all stored energy is not potential energy. For example, the energy stored in batteries and firecrackers is in the form of chemical energy.

A. Tick the most appropriate answer.

Question 1.
The amount of energy required to raise the temperature of I g of water by 1°C is called
a. 1 joule
b. 1 newton
c. 1 calorie
d. 1 watt
Answer:
c. 1 calorie

Question 2.
A child riding a bicycle possesses
a. potential energy.
b. heat energy.
c. kinetic energy.
d. sound energy.
Answer:
c. kinetic energy.

Question 3.
When a ball is thrown vertically upwards, the gravitational potential energy of the ball
a. increases
b. decreases
c. remains same
d. none of these
Answer:
a. increases

Question 4.
Which form of energy is possessed by a stretched spring?
a. Chemical
b. Elastic potential
c. Muscular
d. Heat
Answer:
b. Elastic potential

Question 5.
Which transformation of energy takes place in a door bell?
a. electrical energy into kinetic energy
b. electrical energy into sound energy
c. chemical energy into electrical energy
d. nuclear energy into light energy
Answer:
b. electrical energy into sound energy

B. Fill in the blanks.

Question 1.
The SI unit of energy is ……………
Answer:
The SI unit of energy is joule.

Question 2.
The stretched rubber band of a catapult possesses …………. energy.
Answer:
The stretched rubber band of a catapult possesses elastic potential energy.

Question 3.
The energy of the food that we eat is stored as …………… energy.
Answer:
The energy of the food that we eat is stored as chemical energy.

Question 4.
………….. energy is produced when you strike a drum.
Answer:
Sound energy is produced when you strike a drum.

Question 5.
Plants use the ………….. energy from the sun to prepare their food.
Answer:
Plants use the light energy from the sun to prepare their food.

C. Match the columns.

1. 1 Calorie	a. sound energy
2. Burning	b. magnetic energy
3. Coiled spring in a watch	c. heat energy
4. Vibrating bodies	d. 4.186 joules
5. Magnets	e. elastic potential energy

Answer:

1. 1 Calorie	d. 4.186 joules
2. Burning	c. heat energy
3. Coiled spring in a watch	e. elastic potential energy
4. Vibrating bodies	a. sound energy
5. Magnets	b. magnetic energy

D. Write true or false. Correct the false statements.

Question 1.
The energy possessed by a body by virtue of its position is known as kinetic energy.
Answer:
False.
The energy possessed by a body by virtue of its position is known as gravitational potential energy.

Question 2.
Both kinetic and potential energy are called mechanical energy.
Answer:
True.

Question 3.
The energy stored in fire crackers is in the form of magnetic energy.
Answer:
False.
The energy stored in fire crackers ¡s in the form of chemical energy.

Question 4.
Nuclear energy is released when the nucleus of an atom splits.
Answer:
True.

Question 5.
Energy can neither be created nor destroyed.
Answer:
True.

E. Answer the following in a word or two or in a sentence.

Question 1.
What do you understand by the term energy?
Answer:
Energy ¡s the capacity of a body to do work.

Question 2.
Define kinetic energy and give an example of a body possessing kinetic energy.
Answer:
Kinetic energy of a body is the energy possessed by it due to its motion or movement.
Examples : A child riding a bicycle, a moving bus, moving air (wind), flowing water — all possess kinetic energy.

Question 3.
Give an example where electrical energy gets converted to sound energy.
Answer:
Doorbell.

Question 4.
Name the energy possessed by a flowerpot placed at the rooftop of a building
Answer:
Gravitational potential energy.

Question 5.
State the law of conservation of energy.
Answer:
The law of conservation of energy states that energy can neither be created nor destroyed, but it can be transformed from one form to another.

F. Answer the following in detail.

Question 1.
Describe different units of energy. What is the relationship between calorie and joule?
Answer:
Calorie and joule are different units of energy. A calorie is defined as the amount of heat energy required to raise the temperature of 1 g of water by 1 °C. On the other hand, one joule is defined as the amount of work done when a force of 1 N causes a displacement of 1 m in a body in the direction of the force. The relationship between calorie and joule is, 1 Calorie = 4.186 joules.

Question 2.
What is meant by mechanical energy ? Explain in detail.
Answer:
The energy possessed by a body due to the work done on it is called as mechanical energy. Work is done on a body when the body is displaced. So, the energy gained by a body due to its state of motion (during displacement) or due to its position (at the end of displacement) is known as mechanical energy.

Mechanical energy is of two types –
(i) Kinetic energy – Energy possessed by a body due its motion or movement.
Example : Flowing water, wind possess kinetic energy.

(ii) Potential energy – Energy possessed by a body due to its position.

It is of two types –
(a) Gravitational potential energy – Energy possessed by a body due to its raised position (height). Work is done to raise a body to a certain height against the pull of gravity.
Example : Mango on a tree, flower pot placed on a balcony possess gravitational potential energy.

(b) Elastic potential energy – Energy that gets stored in a body when the body is stretched, compressed or bent.
Example : A stretched bow, a winded spring of toy and coiled spring used in watches possess stored elastic potential energy.

Question 3.
Explain why water stored in a dam has potential energy.
Answer:
An object is said to have gravitational potential energy due to
its raised position (height). It is because work has to be done to raise a body to a certain height against the pull of gravity. Thus, when water is raised to a height in a dam, it gains gravitational potential energy.

Question 4.
What do you understand by the transformation of energy? Explain by giving an example.
Answer:
The change of one form of energy into another is known as the transformation of energy. For example, when a car engine runs, the chemical energy of the fuel transformed into kinetic, heat and sound energy.

Question 5.
Explain the conservation of energy in a roller coaster.
Answer:
In a roller coaster, the sum of potential energy and kinetic energy of the car at any point is always constant. So, the total energy is always conserved. When the car is at the top of the coaster, it has its maximum potential energy. When the car is at the bottom of the coaster, it has its maximum kinetic energy. When the car is going up or coming down, the potential and kinetic energies readily change from one form to another.

G Identify the different forms of energy possessed by the bodies given in the following pictures.

Answer:

1. Gravitational potential energy.
2. Heat energy.
3. Light energy.
4. Elastic potential energy.
5. Kinetic energy.
6. Nuclear energy.

Think And Answer

Question 1.
A dog and a horse are running at the same speed. Who has more kinetic energy and why?
Answer:
The horse possesses more kinetic energy as the mass of horse is greater than that of the dog.

Question 2.
A body is thrown vertically upwards. What happens to its kinetic energy at its highest point?
Answer:
When the ball reaches at the highest point, its kinetic energy becomes zero.

Question 3.
The sum total of energy in this universe is constant. Justify this statement.
Answer:
The law of conservation of energy is true for all the bodies in the universe and for all forms of energy. Whenever one form of energy disappears, an equivalent amount of energy in another form appears.

Projects & Activity

Activity : To solve the crossword with the help of given clues
ACROSS
3. A form of energy that causes a sensation of hotness and coldness.
5. This energy is produced when a force causes a body to vibrate.
7. This energy is produced due to the flow of electric charge through a substance.
8. This energy is released when chemicals are burned or when they undergo a chemical change.
DOWN
1. The form of energy stored in magnets.
2. This energy is possessed by a body due to the work done on it.
4. A form of energy possessed by a body by virtue of its position.
6. This energy is released when an atom splits.
9. A form of energy that enables us to see objects around us.
Answer:

Living Science Physics Class 7 ICSE Solutions