Work, Power and Energy

Work, Power, and Energy

Learning Outcome

  • Relation between work and energy.
  • Relation among work, force, and displacement.
  • Kinetic and potential energy.
  • Transformation of energy in its source.
  • Contribution of the sources of energy regarding economic, social, and environmental influence.
  • Relation between transformation of energy and conservation of energy.
  • Transformation of energy and how its uses hamper the balance of environment.
  • Effective use of energy in developing activities.
  • Effective and safe use of energy.
  • Mass energy relation.
  • Explain the power.
  • Measure the efficiency.

4.1 Work

What is work?

If because of force-displacement happens then the product of force and component of displacement at the direction of force due to force is work.

Work is the product of applied force on a body and its displacement along the direction of force.

Unit of work: J (Joule)

Dimension of work, [W] = ML2T-2

What is Joule?

If due to the appliance of one newton force at the direction of force the application point of force moves 1 metre than it is 1 joule of work.

What is positive work?

If due to force the application point of force moves along the direction of force or the component of displacement is towards the direction of force then it is said to be work done by force or positive work.

What is negative work?

If due to force the application point of force moves in the opposite direction of force or the component of displacement is at the opposite direction of force then it is said to be work done on force or negative work. 

What do you mean by the work 50 J?

The work measuring 50 J means 50 m of displacement of a body towards the direction of a force measuring 1 N. It further means 1 m of displacement of the body toward the direction of a force measuring 50 N.

4.2 Energy

Unit of energy: J (Joule)

Dimension of energy = ML2T-2

4.3 Different form of energy

Kinetic Energy

Kinetic Energy:
A moving object due to its motion acquires ability to do work which is known as kinetic energy.


1. A young man of mass 60 kg start running from the ground floor and reach the roof with the velocity of 30 m/min, find the kinetic energy of the young man? [Ans: 7.5 J]

Potential Energy

What is potential energy?
The energy that an object gains from the change of its different parts or its position change with respect to the surroundings is called the potential energy of that object.

4.4 Sources of Energy

What is the main source of energy?
The main source of energy is sun.

Uses of solar energy

  • Solar cell is used to provide electricity for an artificial satellite. This is why an artificial satellite can rotate on its orbit for a long time.
  • Various electric devices, like pocket calculator, pocket radio, electric clock etc can be run by solar energy.
  • Nowadays even in the villages, offices and households of our country uses of electricity produced by solar panel.

4.5 Conservation and Transformation of Energy

4.6 Relation between mass and energy

4.7 Power

What is power?
The rate of work done in a unit of time by a person or source is called power.

Unit of Power: W (Watt).


The capacity to do 1 joule work in 1 second is 1 watt.

4.8 Efficiency

The ratio of the amount of work we get from an engine given is its efficiency.

Effective Energy:
The energy that we get from an engine is its effective energy.

What do you mean by 70% efficiency of a pump?
70% efficiency of an engine means 100 J input of energy in the engine yields 70 J efficient energy and the rest of 30 J energy is wasted.

4.9 Role of Energy in Development Activities

There is a very close relationship between the development of a country and the use of energy. To speak the truth, the use of energy may be considered as the first parameter to see how developing a country is.

We should pay our first attention to education for the development of our country. A lot of students in our country are studying in schools, colleges, and universities. We have to ensure an adequate supply of electricity to run these institutions properly. They need light for studying at night and their studies are hampered if the electricity supply is not ensured. Laboratories are to be used and computers and networks are to kept active for higher education, and which has no alternative other than the supply of electricity.

Agriculture plays an important role in the economy of our country. As the country is small, the amount of suitable agricultural land is less, and it is further decreasing. Our country has achieved self-sufficiency in food by growing two or more crops in this agricultural land. For this reason, arrangements for irrigation are to be made in the agricultural land without waiting for natural agriculture alone. Without energy supply, this is not possible at all. Electricity or fuel is required to run the pumps for irrigation. Fertilizers are needed for agriculture and the necessary production is not possible without electricity and gas supply in fertilizer factories. Tractors are used to cultivate lands and for the processing of crops, the supply of fuel needed has to be ensured for tractors.

After agriculture, energy supply is needed to ensure health services. A healthy environment is needed for a sound body. In a densely populated area like Bangladesh, energy is required for creating a healthy environment and processing wastage. Energy is needed for a pure water supply. Electricity supply can not stop for a single moment for health services in hospitals.

Other than education, agriculture, and health services, energy is a must for the communication system, industries, mills, and factories and creating the infrastructure of a country. That’s why power plants are to be built through proper planning in our country to prevent a shortage of energy in the future. Misuse of energy is to be stopped and search for gas continued in new gas fields. As the requirement of energy supply has increased quite a lot in the country, the establishment of a nuclear power plant may be considered as a possible solution.

Necessary Equations

No. Information Unit


Mathematical Problems

  • A man of mass 70 kg climbs on a mountain of height 200 m. How much work will he do? [Ans: 1.372×105 J]


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About Me

Md. Saifur Rahman

B.Sc (Honors), M.Sc (Chemistry)

Former Principal of South Point School and College, Dinajpur.

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