Work, Energy

Work, Energy and Power – Physics Summary

Work, Energy, and Power are inter-related and are often used together in as much as they have different methods of deriving or solving practice questions with their formulas respectively. In this article, Work, Energy, and Power, you will learn their definitions, formulas and how they are been applied in solving examination questions.


When a force acts on an object and the object moves in the direction of force, then work is said to be done. Work done by the force is equal to the product of the force and the displacement of the object in the direction of a force.

Displacement has to do with the distance of the force applied to the desired end. (Displacement is same as distance)

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W = F × S

W denotes work done, F denotes Force and S denotes distance.


1) Lifting a Load: If a boy of mass M (Kg) moves up a set of steps of total height H, lifting his body against the force of gravity, which acts in a vertical direction. The work done by the boy is equal to the product of the weight and height.

W = mgh

W = m × g × h

2) Falling Body: When a ball falls freely from the height of a building, the force of gravity does work on the body. A body of mass “M”, falls through a vertical height “H”, work done by gravity on the ball is given by

W= mgh

W = m × g × h



It is defined as the ability or capability to do work.

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Types of Mechanical Energy

Potential Energy (PE): It is stored energy or anything possessed by a body by virtue of its position or state. A body may have potential energy due to its position in a force field. If the force field is the gravitational field, the body is said to possess gravitational potential energy.

Egp = mgh

[– energy, G – gravitational force, – potential energy]

Examples of Potential Energy:

  1. Magnetic potential energy (an example of a magnet)
  2. Electrical potential energy (an example of battery- positive and negative).
  3. Chemical potential energy (example of fuel etc.).
  4. Gravitational potential energy (a falling body).
  5. Elastic potential energy (elastic spring).

Kinetic Energy (KE): Energy possessed by a body by the virtue of its motion. Kinetic energy depends only on the mass and velocity of the body. The kinetic energy of a body in motion is given by

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K.E = 1/2 mv²

– mass, V– velocity.


It is defined as the time rate of doing work.

Power = Work done ÷ Time