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Power of a body is defined as the rate at which the body can do the work.
Average power, 38675.png
Instantaneous power, 38668.png
[as 38661.png]
i.e., power is equal to the scalar product of force with velocity.


Important Points
  • Relations between different units:
    1 W = 1 J/s = 107 erg/s
    1 hp = 746 W
    1 MW = 106 W
    1 kW = 103 W
  • If work done by the two bodies is same, then power ∝ 1/time, i.e., the body which performs the given work in lesser time possesses more power and vice versa.
  • As power = work/time, any unit of power multiplied by a unit of time gives the unit of work (or energy) and not power, i.e., Kilowatt-hour or watt-day are units of work or energy.
  • The slope of work–time curve gives instantaneous power (Fig. 14).
    As P = dW/dt = tanθ
Fig. 14
  • Area under power–time curve gives the work done as
    ∴  38581.png = Area under P-t curve

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