Question

Derive the expression for work done when-

The displacement is in the direction of the force.

Answer 1

A wooden block is kept on a table. When a force of magnitude F acts on the block, it gets displaced through a distance S in the direction of the applied force, as shown in the given figure.

The magnitude of work done is given by the product of force (F) and displacement (S) in the direction of force.

Let W be the work done on the block.

∴ Work = Force × Displacement

Work has magnitude only. It has no direction.

Unit of Work

To obtain the unit of work, we substitute the SI units of force i.e., N, and distance i.e., m, in the equation of work.

W = N × m = Nm

Hence, the unit of work is Nm.

In the honour of physicist James P. Joule, the SI unit of work is written as Joule (J).

Hence, 1 J = 1 Nm

1 Joule is defined as the amount of work done by a unit force such that it displaces an object by a distance of 1 m.