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Mechanical Energy & Work

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- Mechanical Energy & Work

Energy allows us to do useful jobs.

There are many different kinds of energy; mechanical energy is potential and kinetic.

Work

If an object moves due to the application of a force then work is being done on it.

Work done = force x distance in direction of the force

The unit of energy is the joule.

1 J = 1 N x 1 m = 1 kg m2 s-2

- Note:
- 1.Object must move for work to be done ie no work done pushing against a wall.

Work done = 20 x 10 cos 30 = 173 J

To lift the book onto the table I need to exert a force equal to its weight for a distance equal to the height of the table.

Work done = weight x height

W = mgh

This is stored as gpe in the book.

Note: we arbitrarily take the floor as a zero for gpe.

Strictly,Dgpe = mgDh

This formula applies only for small changes in height

i.e g is assumed constant.