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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:**