Concept of Work and Energy (Part – 2)

Potential Energy :-

It is related to stored energy. The potential energy of a object is due to its position.

For example :- When a ball falls from a height its potential energy converts into Kinetic energy but when ball is not thrown, the energy stored in it is called Potential Energy.

Let m be a mass of an object, falling from a height ‘h’. Let the work done ‘W’on object against gravity.

Work Done = Force * Displacement

W = F * s

Where F = m * g

So. W = m g h

Where m = mass

g = gravitational force

h = height

Work done by the object is equal to Potential energy.

E = m g h

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Law of conservation of Energy

We know that Energy neither be created nor be destroyed. It may changes from one form to another. So in case of conservation of energy, the energy converts its form from potential energy to kinetic energy or kinetic energy to potential energy .

According to conservation law of energy the total mechanical energy is same in any situation. So we can say mechanical energy is constant for all situations.

Mechanical Energy = Potential Energy + Kinetic Energy

Mechanical Energy = Constant

Potential Energy + Kinetic Energy = Constant

For example :- If we are throwing a ball from a height before thrown the object have only potential energy when we throw that ball, the potential energy start converting in Kinetic energy but the total mechanical energy does not changes.

Mechanical Energy = Potential Energy + Kinetic Energy

M.E. = m g h + ½ m v^2

Potential Energy + Kinetic Energy = Constant

m g h + ½ m v^2 = Constant

In this situation the loss in potential energy = gain in kinetic energy

Introduction of Power

We know that we can do work according to our capacity. The machines can do maximum work according to its capacity so we generally see that in same time periods the production of machines are different. In other examples the different types of cars have different speed capacity so it can run on different speeds.

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Definition of Power

The capacity of doing work of any machine or human, is called Power.

If a work done ‘w’ is completed in time ‘t’ then power is

Power = Work / Time

P = W / t

Units of Power

Unit of power is J / Sec or Watt

1 Watt = 1 J / Sec

1 Kilowatt = 1000 watt

1 KW = 1000 W

1 KW = 1000 J / Sec

If the rates are different in different interval of time, in this case we use concept of average power.

Commercial Unit

Joule is very small unit of Power. We are not generally used this unit in commercial purpose. So we use KW hour, it means power consumption for an hour. It is generally said as ‘Unit’

1 kW h = 1 kW * 1 h

= 1000 W * 3600 Sec

= 3600000 J

1 kW/h = 3.6 * 10^6 J

In our day today life we used kW h

Electricity consumption in our house is expressed in units.

1 units = 1 kW h

Milan Tomic

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