ICSE Living Science Physics for Class 6 Solutions Chapter 6 Work and Energy
Check Your Progress (Page 62)
Answer the following.
Question 1.
What is the amount of work done in pushing a wall ?
Answer:
No work is done in pushing a wall because even though the force is applied, there is no displacement.
Question 2.
State the formula used to calculate the work done.
Answer:
Work = Force * Displacement or W = F x s
Question 3.
What is the SI unit of work ?
Answer:
SI unit of work is newton metre (Nm). It is also called as joule (J). .
Question 4.
If either of the displacement or the force applied changes, how does the amount of work done get affected?
Answer:
Displacement and force applied are directly proportional to the work done. Greater the magnitude of force applied, more is the work done. Greater is the displacement, more is the work done.
Question 5.
A force of 45 N displaces a chair by 0.5 m. What is the amount of work done ?
Answer:
Force, F = 45 N
Displacement, s = 0.5 m Work done, W = ?
We know that,
W = F x s = 45 x 0.5 Nm = 22.5 Nm or 22.5 J
Check Your Progress (Page 66)
State if the following statements are true or false. Correct the statement if it is false.
Question 1.
A coiled spring in a watch has gravitational potential energy.
Answer:
False. A coiled spring in a watch has elastic potential energy.
Question 2.
Sound is a form of energy produced by a vibrating body.
Answer:
True
Question 3.
Both kinetic and potential energy are called mechanical energy.
Answer:
True
Question 4.
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 potential energy.
Question 5.
The SI unit of energy is newton.
Answer:
False. SI unit of energy is Joule (J).
A. Tick the most appropriate answer.
Question 1.
In which of the following situations no work is said to be done ?
a. Drawing water from a well
b. Kicking a ball
c. Climbing up a hill
d. Pushing a wall
Answer:
d. Pushing a wall
Question 2.
No work is said to be done if the angle between the directions of force and displacement is
a. 0°
b. 90°
c. between 0° and 90°
d. 180°
Answer:
b. 90°
Question 3.
If the force applied on a body decreases, then the work done on it will
a. decrease
b. increase
c. remain the same
d. be zero
Answer:
a. decrease
Question 4.
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 5.
Which form of energy is possessed by a stretched spring?
b. Elastic potential
d. Heat
Answer:
b. Elastic potential
B. Fill in the blanks.
Question 1.
The SI unit of work is ………….
Answer:
The SI unit of work is joule (J).
Question 2.
The energy possessed by the streched rubber band of a catapult is in the form of ……………
Answer:
The energy possessed by the streched rubber band of a catapult is in the form of elastic potential energy.
Question 3
………….. energy is also used in the treatment of cancer.
Answer:
Nuclear energy is also used in the treatment of cancer.
Question 4.
The sources of energy that deplete on use and cannot be used again are called …………. sources of energy.
Answer:
The sources of energy that deplete on use and cannot be used again are called non-renewable sources of energy.
Question 5.
A series of energy transformations is called an ………….
Answer:
A series of energy transformations is called an energy chain.
C. Match the following.
| Column A | Column B |
| 1. Work done | a. sound energy |
| 2. Burning of charcoal | b. solar energy into electrical energy |
| 3. Coiled spring in a watch | c. heat energy |
| 4. Vibrating bodies | d. force X displacement |
| 5. Solar cells | e. elastic potential energy |
Answer:
| Column A | Column B |
| 1. Work done | d. force X displacement |
| 2. Burning of charcoal | c. heat energy |
| 3. Coiled spring in a watch | e. elastic potential energy |
| 4. Vibrating bodies | a. sound energy |
| 5. Solar cells | b. solar energy into electrical energy |
D. State if the following statements are true or false. Correct the statement if it is false.
Question 1.
Work is said to be done only if a force is applied on a body.
Answer:
False. Work is said to be done only if a force is applied on a body and the body gets displaced.
Question 2.
If a car and a motorcycle are running at the same speed, then both will have same kinetic energy.
Answer:
False. If a car and a motorcycle are running at the same speed, then both will not have same kinetic energy.
Question 3.
The energy stored in fire crackers is in the form of magnetic energy.
Answer:
The energy stored in fire crackers is in the form of chemical \ energy.
Question 4.
Nuclear energy is released when the nucleus of an atom energy.
Answer:
True
Question 5.
Coal and petroleum are renewable source of energy.
Answer:
False. Coal and petroleum are non-renewable source of energy.
E. Answer the following in a word or two or in a sentence.
Question 1.
What will be the work done by a force acting on a body if displacement of the body is zero ?
Answer:
Zero (no work d(}ne).
Question 2.
Give an example in which electrical energy gets converted “to sound energy. ~
Answer:
Door bell.
Question 3.
Name the energy possessed by a flowerpot placed at the rooftop of a building.
Answer:
Gravitational potential energy.
Question 4.
Name the energy transformations that take place in a dry cell.
Answer:
Chemical energy into electrical energy.
Question 5.
Give a method by which we can save energy.
Answer:
Use compact fluorescent lamps (CFL) and light – emitting diodes (LED) instead of incandescent bulls as CFLs use 80% less
energy and LEDs use 90% less electricity than regular bulbs.
F. Answer the following in short.
Question 1.
State the factors responsible for work done by a body.
Answer:
There are three factors responsible for work to be done by a body:
- A force must be applied on the body.
- The body should move from its position of rest.That is, there should be a displacement, or there should be a change in the shape or size of the object.
- The displacement must be because of the force applied.
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.
How do we get electricity from wind ?
Answer:
Wind is moving air which possesses kinetic energy. This energy is used by windmills to turn the shafts of generators to generate electricity.
Question 4.
What are renewable sources of energy ? Give two examples.
Answer:
The sources of energy that do not get depleted on use and can be used again and again are called renewable sources of energy. Examples : The sun, wind and water are renewable resources of energy.
G. Answer the following in detail.
Question 1.
Give reason why water stored in a dam has potential energy.
Answer:
Potential energy is the energy possessed by a body due to its position or height of the body. Water stored in a dam has potential energy because work is done to raise the water to a certain height against the pull of gravity. The is acquired as potential energy.
Question 2.
What is meant by ntechanical 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 –
- Kinetic energy – Energy possessed by a body due its motion or movement. Example : Flowing water, wind possess kinetic energy.
- 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 the various energy transformations that take place when you run the engine of a car.
Answer:
According to the law of conservation of energy, energy can neither be created nor destroyed. It can be transformed
converted from one form to another. When a car engine runs, the chemical energy of the fuel changes into kinetic energy, heat energy and sound energy.
Question 4.
Define an energy chain. Discuss the various transformation that take place during a water cycle.
Answer:
Series of energy transformations is called as energy chain. In a water cycle, the heat energy of the sun evaporates water from water bodies. After evaporation, this water forms clouds and the clouds brings rains. The mechanical energy of water has been caused due to solar energy (heat energy of sun).
Question 5.
Describe the work-energy relationship by giving a suitable example.
Answer:
Energy is the ability of a body to do work. So, there is a direct relationship between energy and work. For example, when an object is at a height from the ground, it has a certain amount of potential energy. When we drop the object, it falls because of the force of gravity. White falling down, its kinetic energy is gradually used up until it becomes zero (just when the object touches the ground). At any point during its fall, the amount of kinetic energy which is used up by the body is equal to the distance it has travelled (work done). So, amount of work done by a body = amount of energy change in the body.
H. Give reasons for the following.
Question 1.
No work is done on a suitcase if a man holding it walks on a horizontal platform ?
Answer:
When a man is walking holding a suitcase, the suitcase moves. But the force applied (force of gravity) on the suitcase is in the vertically upward direction (against the gravity), whereas the displacement is in the horizontal direction on platform. A vertical force can never cause a horizontal displacement. So the displacement of the suitcase is not due to the force acting on it. Therefore, no work is done.
Question 2.
Work is said to be done if a man with a suitcase held in his hand climbs a staircase.
Answer:
When a man with a suitcase held in his hand climbs a staircase, he is applying force against the gravity, to raise it to a height. The suitcase has been displaced because of the force applied. Therefore, work is said to be done.
I. Solve the following numerical problems.
Question 1.
Find out the work done when a force of 80 N displaces a body through 5 m.
Answer:
Force, F = 80 N
Displacement, s = 5 m Work done, W = ?
Work done, W = F x s = 80 x 5 = 400 Nm or 400 J
Question 2.
Calculate the work done in pushing a cart through a distance of 10 m against the force of friction which is equal to 120 N.
Answer:
Displacement, s = 10 m
Force, F = 120 N
Work done, W = ?
We know that,
W = F x s = 120 N x 10 m
= 1200 Nm or 1200 J
Question 3.
If 1000 J of work is done by a machine to move a body through a distance of 20 m, then find the force applied on the body.
Answer:
Work done, W = 1000 J
Displacement, s = 20 m
Force, F = ?
We know that,
W = F x s
⇒ F = \(\frac {W}{s}\) = \(\frac {1000Nm}{20m}\) [Nm = J]
= 50 N
Question 4.
A boy applies a force of 25 N to push a box. Calculate the displacement of the box if the total work done is 225 J.
Answer:
Force, F = 25 N
Work done, W = 225 J
Displacement, s = ?
W = F x s
s = \(\frac {W}{F}\)
= \(\frac {225 Nm}{25N}\) [Nm = J] = 9m
J. Sort out the following forms of energy into stored form and energy in action form.
Question 1.
Chemical energy
Answer:
Stored form
Question 2.
Heat energy
Answer:
Energy in action form
Question 3.
Light energy
Answer:
Energy in action form
Question 4.
Nuclear energy
Answer:
Stored form
Question 5.
Sound energy
Answer:
Energy in action form
Question 6.
Magnetic energy
Answer:
Stored form
Living Science Physics Class 6 ICSE Solutions