Page 72 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

EXERCISE 5 : Work, power & energy

Definitions: When a force is applied to a body and there is a displacement of that body along in the direction of
force then the work is said to be done by that force. The work done is a scalar quantity.
Work done is denoted by W.

W= F X S

Units, Calculation & Application
The SI unit of work is Joule (J) or N m and the CGS unit is erg. The calorie (cal) is also a unit of work.
1 erg = 10−710−7Joule = 10−710−7 N m

1 cal = 4.186 Joule

The SI unit of work is joule (J). Joule is defined as the work done by a force of one Newton causing a displacement
of one meter. Sometimes, Newton-metre (N-m) is also used for measuring work.
There are many examples of work done in our everyday life. For example, a horse pulling a plow through the
field, a father pushing a grocery cart in a shopping mall, or a student lifting a bag on his back on his back or his
shoulder full of books and many more.
POWER: Power is the amount of energy that is transferred in a unit of time.
Work done / Time taken = Force x (Displacement / Time taken)

Since Work done / Time taken = Power, and Displacement / Time taken = Velocity, we can simplify the formula
to: Formula: Power = Force (N) x Velocity in the direction of the force (m/s) Simplified formula: P = Fv. SI Unit:
Watt (W).
ENERGY: Energy can be defined as the ability to do work.
The equation developed by Albert Einstein, which is usually given as E = mc , showing that, when the energy of
2
a body changes by an amount E (no matter what form the energy takes), the mass (m) of the body will change
by an amount equal to E/c .
2
There is a significant difference between work and energy. Work is the transferring of an amount of energy with
the help of a force covering a particular distance in a direction. Energy is also referred to as the force that works
at a certain distance.

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CITS : WCS - Mechanical - Exercise 4