Work:

In our daily life, we do many activities which are called as work and are related with energy and power. Activities like watching movies, talking with friends, humming a tune are not considered as a work. Work is to be done only when force is acted on the object or the object is displaced e.g. pushing a shopping trolley or cart pulled by a person etc.

Work is a product of force action on an object and the displacement of an object after the application of force.

Consider Force F is applied on an object and the object is displaced through a distance s, then the work done in the direction of force is w.

            Work = Force x displacement

            W = F x s

Work is equal to the magnitude of the force and the distance moved by the object in the direction of force. Work has only magnitude and no direction.

Unit of work = Newton meter or joule

Work is positive = when the force acts opposite to the direction of displacement

Work is negative = when the force is in the direction of displacement.

Energy:

An object possesses energy when it has a capability to do work. Activities like cooking food, dancing on music, Singing a song requires energy.

Energy lost – object does the work

Energy gain – object on which work is done

Unit of energy = joule

Power:

The rate of doing work or the rate of transfer of energy is called power. Power measures the speed of work done.

Consider an object does a work W in time t, then power is given by,

            Power = work/time

            P = W/t

The Unit of power = watt in honor of James Watt having the symbol W.

            1 watt = 1 joule/second

Larger rates of energy transfer are kilowatts (kW).

            1 kilowatt = 1000 watts

            1 kW = 1000 W

            1 kW = 1000 J/s

Power of an object may vary with time as the object may be doing work at different rates at different intervals of time. So, the concept of average power is useful which is obtained y dividing the total energy consumed by the total time taken.

Calculations:

Ex-1: Work done on an object by a force would be zero if the displacement of the object is ………….

a)      One

b)     Zero

c)      Twice

d)     None

Answer: Work is equal to the magnitude of the force and the distance moved by the object in the direction of force. Work done on an object by a force is Zero here so the displacement of the object is also zero.

Ex-2: An object having capability to do work is said to possess ………..

a)      Mass

b)      Pressure

c)      Weight

d)     Energy

Answer: An object possesses energy when it has a capability to do work.

Ex-3: Work is defined as the magnitude of the force multiplied by the ……………..moved by the object.

a)      Distance

b)      Mass

c)      Weight

d)     Pressure

Answer: Work is equal to the magnitude of the force and the distance moved by the object in the direction of force.