Subject: Science

The rate of doing work is called power. It is a scalar quantity. Its SI unit is Watt (W). Another common unit of a power is horsepower. Horsepower is related to watt as:

1 horsepower = 746 W = 750 W approximately.

Power =

1 kilowatt (KW) = 1000 watt

1 megawatt (MW) = 1000000 watt

1 horsepower (HP) = 750 watt (approx.)

The power is one watt when one joule of work is done in one second.

**Relation between Work, Energy and Power**

Work, energy and power are interrelated terms. Actually, the capacity to do work is a power which comes from energy. When a person does a work then he loses some amount of energy. We get energy from food. Our body stores chemical energy and transforms it into muscular energy. We use that muscular energy to do work.

The rate of doing work is power. If we work faster then power is increased. If higher energy is applied to do work then work done becomes faster and power will also get increased. So, work, energy and power are interrelated terms.

- The rate of doing work is called power.
- Its SI unit is Watt (W).
- 1 kilowatt (KW) = 1000 watt
- 1 megawatt (MW) = 1000000 watt
- 1 horsepower (HP) = 750 watt
- Work energy and power are interrelated terms.

- It includes every relationship which established among the people.
- There can be more than one community in a society. Community smaller than society.
- It is a network of social relationships which cannot see or touched.
- common interests and common objectives are not necessary for society.

The rate of doing work is power. The SI unit of power is watt (W).

What is one watt? Write the relation of watt with kilowatt, megawatt and horsepower.

If one joule of work is done in 1 second, it is said to be one watt. The relation is:

KW = 1000watt (10³ watt)

1MW = 1000 000 watt (10^{6} watt)

1 HP = 746 watt (approximately 750 watt)

What is the relation among work, energy and power?

The relation among work, energy and power are:

- The capacity to do work is called energy.
- The rate of doing work is called power.

Power is defined as the rate of doing work.

A body is said to have one watt power when it does one joule of work in one second.

A body is said to have unit power if it does unit work in unit time.

A 60 kg person climbs stairs of total height 20 m in two minutes. Calculate the power of the person.

\begin{align*} \text {Solution,} \\ \text {The work done in climbing a height of 20m is} \\w &= m \times g \times h \\ &=60 \times 9.8 \times 20\\ &= 11760 J\\ \text {Power delivered is} \\ P &= \frac wt \\ &= \frac {11760}{120} \\ &= 98\: W \\ \text {Therefore, the power of person is} \: 98 \: W \\ \end{align*}

A crane lifts a load of 75 N to the height of 20 m in 100Sec. Calculate the power of the crane.

\begin{align*} \text {Solution,} \\ \text {force} \: (F) &= 75 N \\ \text {distance} \: (d)&= 20 m \\ \text {time} \: (t)&= 100 sec \\ \text {power}\:(P) =?\\ \text {Now,} \\ p &= \frac wt \\ &= \frac {75 \times 20}{100} \\ &= 15\: J \\ \text {Thus, the power of crane is}\: 15\: N\\\end{align*}

An electric heater has power 2 Kw. in 60 seconds how many joules of heat is produced?

\begin{align*} \text {Here,} \\ \text {Power} \: (P) &= 2\: KW = 2\times 1000 = 2000\: J/s \\ \text 60\: \text {seconds, electrical energy is converted into heat energy,} \\ &= 2000 \times 60 \\ &= 120, 000\: \text {Joule} \\ &= 120\: KJ \\ \end{align*}

A crane can lift a load of 3000 N through a height of 5 m in 10 seconds. Find its power.

\begin{align*} \text {Here,} \\\text{Force}\:(F)&= 3000\: N\\\text{distance}\:(d)= 5\:m \text {Work done} \: (W) &= F \times d = 3000 \times 5 = 15000\:j \\ \text {Time taken}\: (T) &= 10 s \\ \text {Power} \: (p) = ? \\ \text {we have,} \\ \text {Power} \: (P) &= \frac WT &= \frac {15000\: J}{10\: s} \\ &= 1500\: J/s = 1.5\: KW \\ \end{align*}

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