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Work Done (OCR GCSE Physics A (Gateway))

Revision Note

Leander Oates

Written by: Leander Oates

Reviewed by: Caroline Carroll

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

  • When work is done on an object, energy is transferred

  • The amount of energy transferred (in joules) is equal to the work done (also in joules)

energy transferred (J) = work done (J)

work-force-object, IGCSE & GCSE Physics revision notes

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

 

 

Calculating Work Done

  • The formula for work done is:

Work done = force × distance

W space equals space F s space

 

  • Where:

    • W = work done in joules (J) or newton-metres (N m)

    • F =force in newtons (N)

    • s = distance/displacement in metres (m)

  • You can rearrange this equation with the help of the formula triangle:

I6htS8Vi_work-triangle-3-igcse-and-gcse-physics-revision-notes

Use the formula triangle to help you rearrange the equation

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, s = 23 m

  • Force, F = 500 N

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

W = F × s

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

W = 500 × 23

W = 11 500 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.

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 energy transferred to 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

W space equals space F s

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

W e i g h t space equals space m g

W space equals space open parentheses m g close parentheses s

  • Note: This is the equation for gravitational potential energy

E space equals space m g h

Step 4: Calculate the work done on the bucket

W space equals space 12 space cross times space 10 space cross times space 15

W 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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    Author
    Reviewer
    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.

    Caroline Carroll

    Author: Caroline Carroll

    Expertise: Physics Subject Lead

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.