Work Done (AQA GCSE Physics)
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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.
Answer:
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
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