**Work Energy and Power**

**Work**

In ordinary conversation the word “work” refers·to almost any kind of physical or mental activity, but in science and mathematics it has .one meaning only. Work is done when a force produces motion. A locomotive pulling a train does work; so does a crane when it raises a load against the pull of the earth. Similarly, a workman who is employed to carry bricks up a ladder and on to a scaffold platform also performs work. On the other hand, the Greek god Atlas, who spent his time supporting the world on his shoulders, must have become very tired, but, technically speaking, he did no work on the world itself, since he merely exerted an upward force on it without moving it.

Nevertheless, when a person holds a heavy load some internal work is done by continuous expansion and contraction of his muscular fibers. artwork is said to be done when the point of application of a force moves and is measured by the product of the force and the distance moved in the direction of the force Work = force x distance moved in direction of force. e SI unit of work is called the joule (J) and is the work done when the point of application of a force of newton ( ) moves through metro (m) in the direction of the for

Larger units used are the kilo joule (kJ) and the mega joule (MJ).

1 kJ = 1000 J (or 103 J)

1 MJ = 1000000 J (or 106 J)

It follows that a locomotive which exerts a force of 9000 N over a distance of 6 m will do 9000 x 6 = 54000 J, or 54 kJ. If we wish to calculate the work done by a man of mass 65 kg in climbing a ladder m high, we multiply his weight, mg, by the vertical height raised.

Thus the work done, assuming g = 10 m/s2, is

(65 x 10) x 4 = 2600 J

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