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Power is the rate of doing work. Or
Power is the rate of transfer of energy.
Note: Work done is the same as energy transferred.
Where work done=Force × Distance
Where mg is the weight of the body and h the height.
The S.I unit of power is watt (W).
Definition:
A watt is the rate of transfer of energy of one joule per second.
Or It is the rate of doing work of 1joule in one second.
Example 1:
An engine raises 20kg of water through a height of 50m in 10 seconds. Calculate the power of the engine.
Solution:
Example 2:
An electric bulb is rated 100W. How much electrical energy does the bulb consume in 2hours.
Solution:
Example 3:
A man uses an electric motor whose power output is 3000W for 1hour. If the motor consumes 1.44×107J of electricity in that time, find the efficiency of the motor.
Solution:
