Work, Energy and Power
Category : 9th Class
Work, Energy and Power
Synopsis
Work is said to be done only when a force displaces an object. The amount of work done by a body is measured as the product of magnitude of the force applied and the distance moved by the body in the direction of the force.
Work is a scalar quantity.
Work = force \[\times \] displacement of the body, W = F \[\times \] S
W = FS \[Cos\,\,\theta \] Where 'S' is the displacement of the object and \[\,\theta \] is the angle between the force and displacement.
W = FS if the displacement is along the force then
\[\,\theta =0\,\,and\,\,cos\,\,\theta =1\]
W = -FS if the displacement is opposite to the force then \[\theta ={{180}^{{}^\circ }}\]and \[Cos\,\theta =-1\].
If the displacement is perpendicular to the force, then the work done is zero\[(\theta =90{}^\circ ,\,\,\cos \,\theta =0)\]
Types of energy:
Kinetic energy: The energy possessed by a body by virtue of its motion is called kinetic energy. If a body of mass m is moving with a velocity v, then its kinetic energy is given as \[K.E.=\frac{1}{2}m{{v}^{2}}\]
Potential energy: The energy possessed by a body by virtue of its position is called potential energy. If a body of mass W is lifted to a height 'h' against gravity 'g; then its potential energy is given as P.E.= mgh
Potential energy is of two types:
(i) Gravitational potential energy: The potential enegrgy of an object due to its height above the earth's surface is called its gravitational potential energy.
(ii) Elastic potential energy: A stretched or compressed object such as a spring or a rubber band has elastic potential energy.
Horse Power = 746 W
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