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Work & Energy (Edexcel GCSE Physics)

Revision Note

Leander Oates

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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-force-object, IGCSE & GCSE Physics revision notes

Work is done when a force is used to move an object

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

Work done = energy transferred

 

  • To calculate the amount of work done or energy transferred for an object, the following formula is used

E space equals space F space cross times space d

  • Where:

    • E = work done or energy transferred in joules (J) 

    • F = force in newtons (N)

    • d = distance in metres (m)

  • This equation can be rearranged with the help of a formula triangle

Work triangle (3), IGCSE & GCSE Physics revision notes

Work done, force, distance 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.

braking-work, IGCSE & GCSE Physics revision notes

Calculate the work done by the brakes in stopping the car.

Answer:

Step 1: List the known quantities

  • Distance, d = 23 m

  • Force, F = 500 N

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

E space equals space F space cross times space d

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

E space equals space 500 space cross times space 23

E space equals space 11 space 500 space straight J

Examples of Work

  • Work is done on a ball when it is lifted to a height 

    • The energy is transferred mechanically from the ball's kinetic energy store to its gravitational potential energy store

Work Done ball, downloadable IGCSE & GCSE Physics revision notes

The weight on the ball produced by the gravitational field does work on the ball over a distance

  • Work is done when a bird flies through the air

    • The bird must travel against air resistance, therefore energy is transferred from the bird's kinetic store to its thermal store and dissipated to the thermal store of the surroundings

Work Done bird, downloadable IGCSE & GCSE Physics revision notes

Air resistance (drag) does work against the bird as it flies through the air

Worked Example

A woman draws a bucket up out of a well. The bucket has a mass of 12 kg when filled with water and the well is 15 m deep. Gravitational field strength is 10 N/kg.

Work Energy Transfer Worked example, downloadable IGCSE & GCSE Physics revision notes

a) Describe the energy transfer involved in raising the bucket out of the well

b) Calculate the work done on the bucket

Answer:

Part (a)

  • Energy is transferred mechanically (a force is acting over a distance)

  • from the kinetic store of the woman (as she pulls the rope)

  • to the gravitational potential store of the bucket (as it is lifted upwards)

Part (b)

Step 1: List all of the known quantities

  • Mass, m = 12 kg

  • Gravitational field strength, g = 10 N/kg

  • Height, h = 15 m

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

E space equals space F space cross times space d

Step 3: Write out the equation for weight and substitute it into the work equation

W space equals space m space cross times space g

E space equals space open parentheses m space cross times space g close parentheses space cross times space d

  • Note: This is the equation for gravitational potential energy

increment G P E space equals space m space cross times space g space cross times space increment h

Step 4: Calculate the work done on the bucket

E space equals space 12 space cross times space 10 space cross times space 15

E space equals space 1800 space straight J

  • The bucket gained 1800 J of gravitational potential energy

Examiner Tips and Tricks

Remember:

  • Changes in speed are related to kinetic energy

  • Changes in height are related to gravitational potential energy

  • Changes in the shape of materials are related to elastic potential energy

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    Leander Oates

    Author: Leander Oates

    Expertise: Physics

    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.