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# What is the difference between Work, Energy and Power: Class 9 CBSE

What is the difference between Work, Energy, and Power Class 9 CBSE: Work is the product of force and displacement in the direction of force, energy is the efficiency of doing work and power is the rate of doing work or the rate of consumption of the energy.Here the detail of the physics terms, Work, Energy, and Power are explained beautifully so that each student could understand basic physics concepts clearly before upgrading to the higher class physics.

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• Definition of the work
• The formula of the work
• Unit of work
• Example of work
• Definition of the Energy
• The formula of the Energy
• Unit of Energy
• Example of Energy
• Work-Energy Theorem
• Definition of the power
• The formula of the power
• Unit of power
• Example of power

### Work Definition:

The work is the product of the force and displacement in the direction of the force or the component of the force,for the complete definition of work, force should be replaced by the component of the force, since force, as well as displacement both, are vector quantities the angle between force and displacement may be 0° to 90°, therefore, one component of force displaces the object in the direction of the force.

In real life the meaning of work is quite different, for example, if somebody is working on a computer then scientifically there is no work done because the computer is not displaced by the worker.

### The formula of the work:

$\fn_cm W=\overrightarrow{F}.\overrightarrow{d}$

$\fn_cm W=F dcos\theta$

Where W is the work done and Fcosθ is the component of the force in the direction of the displacement and d is displacement.

Class 9 students of CBSE are required to remember only that

W= F×d

### Unit of work:

The formula for the work is

W = F.d

The unit of the work done = Unit of the force× Unit of the displacement= Nm(Newton meter) =Joule

1NM is named 1 joule after the name of James Prescott Joule who discovered the relationship between mechanical work and heat transfer.

### Example of work

A force of 50 N on an object displaces it up to the distance of 5m in the direction of the force, find the work done on the object.

Solution:F= 50 N, d = 5 m

W = F.d = 50 ×5 = 250 J

### Definition of the Energy:

Energy is the efficiency or capacity of the doing work, energy has different forms, energy is neither created nor destroyed, and it can be changed from one form to another form. It can also be defined as a transfer of the work.

### The formula of Energy:

There are several types of energy for example mechanical energy, chemical energy, nuclear energy, gravitational energy, etc.

Here we shall discuss the formula of mechanical energy which is of two types

Kinetic energy: Kinetic energy is the capacity to do work by a moving object

Let the mass of the object is m and its velocity is v then kinetic energy  $\fn_cm E_{k}$ is given by

$\fn_cm E_{k}=\frac{1}{2}mv^{2}$

Potential energy: Potential energy is the capacity of doing work by a stationary body due to its specific position.

Let the mass of the object is m and it is displaced to a certain height(h) from the ground of the earth then its potential energy$\fn_cm E_{p}$ is given by

$\fn_cm E_{p}=mgh$

### Unit of Energy:

The unit of energy is the joule same as that of work done

Example of Energy: An object of the mass 50 gm is moving with a velocity of 10 m/s , finds its kinetic energy.

Solution: The kinetic energy of the object  $\fn_cm E_{k}$  is given by

$\fn_cm E_{k}=\frac{1}{2}mv^{2}$

Where m = 50 gm = (50/1000) kg = 0.05 kg and v = 10 m/s

$\fn_cm E_{k}= \frac{1}{2}\times 0.05\times 10\times 10=0.25$

Hence the kinetic energy of the object is 0.25 Joule

Work Energy Theorem: Work is the transfer of the energy,the work done is stored in the form of energy,both work done and energy are interconvertible to each other.The amount of work done depends on how much energy is supplied for doing work.

Let work done is W and energy transfer is ΔE

W = ΔE

### Definition of the power:

Power is the rate of doing work or the rate of the amount of energy released or consumed. Power is measured as the extent of work done within a given time.

### The formula of the power

The power (P) = Work/Time

P = W/T

### Unit of power

The SI unit of the power is a watt

1 watt =1 Joul/second

### Example of power

A bulb of 100 w is kept on up to the time of 5h, then how much work is done by it or energy consumed by it.

Solution:  P= W/T

T = 5h=5×60×60 = 1800s, P= 100 W

100 = W/1800

W= 180000 J

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