# 5.2.1 Work Done

### Work Done

• Work is done when an object is moved over a distance by a force applied in the direction of its displacement
• It is said that the force does work on the object
• If a force is applied to an object but doesn’t result in any movement, no work is done Work is done when a force is used to move an object

#### Examples of Work

• Work is done on a ball when it is lifted to a height above the ground The weight on the ball produced by the gravitational field does work on the ball over a distance equal to the height of the ball

• Work is done when a bird flies through the air Air resistance (drag) does work against the bird as it flies through the air

### Calculating Work Done

• The amount of work that is done is related to the size of the force and the distance moved by the object in the direction of the force
• To calculate the amount of work done on an object by a force the following formula is used

W = F × s

• Where:
• W = work done in Joules (J) or newton-metres (N m)
• F = force in Newtons (N)
• s = distance in metres (m)
• This equation can be rearranged with the help of a formula triangle #### Worked Example

A car moving at speed begins to apply the brakes. The brakes of the car apply a force of 500 N which brings it to a stop after 23 m. Calculate the work done by the brakes in stopping the car.

Step 1: List the known quantities

• Distance, s = 23 m
• Force, F = 500 N

Step 2: Write out the equation relating work, force and distance

Work = F × s

Step 3: Calculate the work done on the car by the brakes

Work = 500 × 23 = 11 500 J ### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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