Note on Power

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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.
.

Very Short Questions

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

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 (106 watt)
1 HP = 746 watt (approximately 750 watt)

The relation among work, energy and power are:

1. The capacity to do work is called energy.
2. 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.

\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*}

\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*}

\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*}

\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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dyne

Newton

watt

joule

750 watt
700 watt
735 watt
755 watt

P=t / w

P=w/t

P=t+w

P=w-t

12 watt
10 watt
14 watt
15 watt

work

speed

power

pressure

• If 1 Joule of work is done in 1 second, the power is said to be ______.

1 watt power

1 joule power

2 erg power

3 pascal power

Power

Energy

Pressure

Work