### Work

- Work done by a constant force is given by the product of the force and the distance moved in the direction of the force.
- The unit of Nm(Newton metre) or J(Joule).
- Work is a scalar quantity.

### Formula

When the direction of force and motion are same, θ = 0

^{o}, therefore cosθ = 1

Work done,

W = F × s

**Example**:

A force of 50 N acts on the block at the angle shown in the diagram. The block moves a horizontal distance of 3.0 m. Calculate the work being done by the force.

**Answer**

Work done,

W = F × s × cos θ

W = 50 × 3.0 × cos30

^{o}= 129.9J

**Example**:

Diagram above shows a 10N force is pulling a metal. The friction between the block and the floor is 5N. If the distance travelled by the metal block is 2m, find

- the work done by the pulling force
- the work done by the frictional force

**Answer**:

(a) The force is in the same direction of the motion. Work done by the pulling force,

W = F × s = (10)(2) = 20J

(b) The force is not in the same direction of motion, work done by the frictional force

W = F × s × cos180o= (5)(2)(-1) = -10J