Power – the rate at which work is done.
From this definition we have the following equation:
Where P is the power, W is the work done measured in joules (J) and t is the time measured in seconds (s).
From the equation we can see that the units for Power can be given as joules per second. The SI unit for power is the watt (W):
One Watt – one joule per second.
Power is a scalar quantity (it has magnitude but not direction).
Worked Examples
Example 1
A lightbulb transfers 3600J of energy per minute. Calculate the power of the lightbulb.
Example 2
An elevator with a weight of 9300N is raised 4m by an electric motor. Calculate the power required from the electric motor to do this in 70s.
This question requires knowledge of Work.
Example 3
A 700kg boat accelerates from rest to 15ms-1 in 22s. Calculate the average power supplied to the boat to reach this velocity.
This question requires knowledge of Work and Kinetic Energy.
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