# What is power?

** In physics power is defined as rate with which work is done.** Power can be calculate in watts or in horse power if you are dealing with electrical power. power have difference equation use in calculation of it , depend on the parameters available just like **equations of motion ** and what you are calculating its power. There are difference types of power, like electrical power, generator power, motor engine power and so on.

That is

Therefore power = where v = velocity, and f = force.

The SI unit of power is called the watt (w) which is the rate of transfer of energy of one Joule per second. That is 1W = 1JS-^{1 }, the large units are the Kilowatt (kw) and megawatt (mw)

1kw = 10^{3}w, 1mw = 10^{6}w

## Sometimes, we use horse power (**h.p) ** unit, to measure power.

Note that **1h.p = 746watt = 0.75kw**

The **units **of energy that is sometime used for electrical energy is called the kilowatt-hour (kwh). This is the energy used by an appliance with a power of one kilowatt in one hour.

**1kwh = 1000w x 3600S = 3.6 x 10 ^{6}J = 3-6MJ**

Examples:

- Calculate the power of pump which lifts 500kg of water through a vertical height of 4 meters in 5 seconds. (assuming g =10MS
^{-2}) - A car travelling at a constant speed of 20ms
^{-1}overcomes a resistance of 300n. What is the horse power of the engine? (take p =3/4kw )

Answers to questions above

- , solution to number one question,

Recall that power =

that is force x distance/time

but F=500N, S = 4, and time = 5s

So work done = 500 x 4 = 2000J, therefore

- To answer number 2 question, let use

Engine power =

Where f = force and v = velocity, therefore

Engine power = 300 x 20 = 6000watts = 6kw

Taking

= 1h.p

6kw = 8h.p.

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