9 th Physics - WORK AND ENRGY In common language, the term work stands for some type of labour, may be physical or mental. But in physics, it is used in a special technical sense. WORK-- Work is said to be done when force produces motion and displaces the body along the line of action of force . The work done W by a force acting on object is equal to the product of the force and the displacement S of the object in the direction of force. Work = Force x displacement W = F . S Work is a scalar quantity. Necessary conditions for work to be done : 1. Force is applied on the body 2. Body is displaced along the direction of application of force. 3. No work is said to be done if any of the two conditions is not satisfied. S.I Unit : W = F x S 1 J = 1 N x 1 m 1 J = 1 N m One joule work is said to be done when a force of one newton displaces a body through one metre along the line of action of force. 1 kJ = 10 3 J 1 MJ = 10 6 J Special Cases : 1.Work done by a force is said to be positive when the force acts in the same direction as that of displacement.
9th Physics - WORK AND ENRGYIn common language, the term work
stands for some type of labour, may be physical or mental. But in
physics, it is used in a special technical sense.WORK-- Work is
said to be done when force produces motion and displaces the body
along the line of action of force . The work done W by a force
acting on object is equal to the product of the force and the
displacement S of the object in the direction of force. Work =
Force x displacement W = F . S Work is a scalar quantity.Necessary
conditions for work to be done : 1. Force is applied on the body2.
Body is displaced along the direction of application of force.3. No
work is said to be done if any of the two conditions is not
satisfied.S.I Unit : W = F x S 1 J = 1 N x 1 m 1 J = 1 N mOne joule
work is said to be done when a force of one newton displaces a body
through one metre along the line of action of force.1 kJ = 103J1 MJ
= 106JSpecial Cases :1.Work done by a force is said to be positive
when the force acts in the same direction as that of
displacement.Eg : Work done by force of gravity on a body falling
under gravity is positive.2.Work done by a force is negative, when
the force acts opposite to the direction of the displacement.Eg :
Work done by frictional force on a moving object is negative3.Work
done by a force is zero, if force is perpendicular to displacement
i.e., no displacement in the direction of force.Eg : Work done on a
satellite revolving around the Earth. 4. Work done by a force is
zero if there is no displacement at all.Eg: No work is done when
one may be pushing a rock and is unable to move it.
POWER: Rate of doing work is known as power. Power is in fact
rate of transfer of energy. Power measures the speed at which work
is done.If an agent does a W work in a time t, then its power P is
given by
Power = work/timeP = W/tPower is a scalar quantity.Average Power
: The ratio of total work done to the total time taken is called
average power.
Average power = total work done / total time taken
S.I Unit : Watt : Power of an agent is said to be one watt if it
can do at the rate of one joule in one second.1 watt = 1 joule/ 1
secondW = J/S 1 kW = 103W 1 MW = 106W Engineering unit of power is
horse power1 H.P = 746 W
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