# NCERT Class 9th chapter 11 Work and energy

Updated Thu, 26 May 2022 04:32 PM IST

## Highlights

If you are looking for topic work and energy in your text book? So this tip is for you, in which article you will get complete information about natural resources.

# Work and energy: Introduction

## What is work

In general, when we do anything, it is said that we are working like cycling, reading, writing, walking etc. The associate work with different type of activities as a weightlifter exert force as he lift a heavyweight
In the language of sciences work is said to be done when a body is displace under the influence of a force along the direction of force.

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 Include In this topic What is Work Measurment Of work Formula of work Unit of Work Special condition Of work done

### Measurement of work done

Immediately there are two factors that must be considered while estimating the amount of work done first is magnitude force
And second one is the displacement produced by the force.
The work done by a force on a body is directly proportional to the force applied and displacement produced by the force.

### Formula of work

Work= force× displacement moved in certain direction
W= F× S
Where is a S is displacement.

### Unit of work

Work measure in joule
1 June = 1 Newton × 1 meter
1J= 1N m

### In CGS

1 erg= 1dyn× 1 cm
Or. 1 eng =1 dyn cm
One newton is equal to 10⁵ dine and one m is equal to 10² cm their 4 1 joule is equal to 10⁷ erg.
1 joule= 10⁷

### Some conditions: special cases of work done

• If the displacement is in the direction of force or force and displacement are parallel to each other the work done is maximum and positive.
W= F- S
• If the displacement is normal to the direction of the force the work done is zero.
W= 0
• If the displacement is in the opposite direction of the force the work done is negative.
W= F- X
Know more:

## Q1-What are the formula work and energy?

Answer- Work can be calculated by multiplying power and distance as follows. W = F × d.

## Q-2 Explain the positive work?

Answer- When force acts in the direction of motion of body work done is positive. When a lawn roller is pulled forward, work done is positive.

## Q-3 Moment of force and work done by a force have the same units. Then, what is the difference between them?

Moment of a force produces rotatory motion in a body whereas when a force does work on a body it produces translatory motion in it.

## Q4-What is work in simple words?

Answer- It is expressed as the product of force and displacement in the direction of force. The unit of Work is Newton metre (Nm) or joule (J). 1 Joule is defined as the amount of work done by force of 1 N when displacement is 1 m. when both the force and the displacement are in the same direction, positive work is done.

## Q5-What is the SI unit of energy?

Answer -The SI unit of energy/work is the joule (J), named for English physicist James Prescott Joule (1818 - 1889).

## Q6-What is the unit of work done?

Answer- In the case of work (and also energy), the standard metric unit is the Joule (abbreviated J). One Joule is equivalent to one Newton of force causing a displacement of one meter. In other words, The Joule is the unit of work.

## Q7-How are the work and energy related?

Answer -Work done = energy transferred. The more work that a force does, the more energy it transfers. The amonunt of work done is simply the amount of energy transferred. W = Change in energy.

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