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9.2 Understanding power

If we run up to the 3rd What is power?
floor we will get tired. As we learnt in the previous unit, a force must be exerted and
But if we walk upstairs displacement must happen in order for work to be done. But the rate at

at a leisurely pace we which work is done is also important. How quickly does a car increase its
textbooks nis edu kz
will not get tired. Why speed? How quickly does water boil in a kettle? Who reaches the finish
line fastest?
is this?
For these and other similar cases, Physics is also interested in the
concept of power. This is used to understand the rate of doing work.
As an example, consider a scenario in which a worker and an excavator
are digging a hole. It is obvious that the excavator will finish this task
in minutes, while the worker can spend a whole day on the same job.
This means that the power of the excavator is greater than the power of
the worker.

REMEMBER! The power of a machine, a person or another physical
body is dependent on the work done and the time it takes to
complete it.
Power is denoted by the letter P. It is equal to the ratio of work done (W)
to the time spent (t), and is calculated according to following equation:

work
power =
time
or
w
P =
t

1 J of work done in 1 s is the definition of the unit of power. This unit of
power is called the watt (W).
1 W = 1 J / 1 s

1 kW (kilowatt) = 1000 W

1 MW (megawatt) = 1 000 000 W

ACT A crane lifts a 2 tonne load to a height of 10 metres in 40 seconds.
Calculate the power of the crane.

Given SI Solution
m = 2 t 2000 kg
h = 10 m
t = 40 s
N = ? Answer:

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