Work done by Power:
A stronger person may do certain work in relatively less time. A more powerful vehicle would complete a journey in a shorter time than a less powerful one. We talk of the power of machines like motorbikes and motorcars. The speed with which these vehicles change energy or do work is a basis for their classification. Power measures the speed of work done, that is, how fast or slow work is done. Power is defined as the rate of doing work or the rate of transfer of energy. If an agent does a work W in time t, then power is given by:
Power = work/time
`"P" = "w"/"t"` ....(i)
The unit of power is watt [in honour of James Watt (1736 – 1819)] having the symbol W. 1 watt is the power of an agent, which does work at the rate of 1 joule per second. We can also say that power is 1 W when the rate of consumption of energy is 1 Js–1.
1 watt = 1 joule/second or 1 W = 1 Js–1. We express larger rates of energy transfer in kilowatts (kW). 1 kilowatt = 1000 watts 1 kW = 1000 W 1 kW = 1000 Js–1. The power of an agent may vary with time. This means that the agent may be doing work at different rates at different intervals of time. Therefore the concept of average power is useful. We obtain average power by dividing the total energy consumed by the total time taken.
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A trolley is pushed along a road with a force of 400 N through a distance of 60 m in 1 minute. Calculate the power developed.