The Work Done Equation - Momentum, Work And Power - BBC Bitesize

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  1. Momentum - Higher
  2. Conservation of momentum - Higher
  3. The work done equation
  4. Power

The work done equation

Work is done when energy is transferred from one store to another. Work is also done when a force causes an object to move. When work is done against frictional forces acting on an object, the object’s temperature increases. For example, a person’s hands warm up when they rub them together repeatedly.

Learn more on work done and energy transfer in this podcast

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Calculating work done

To calculate the work done on an object when a force moves it, use the equation:

work done = force × distance

This is when:

  • work done is measured in joules (J)
  • force is measured in newtons (N)
  • distance moved along the line of action of the force is measured in metres (m)

Note that one joule of work is done when a force of one newton causes a movement of one metre. This means that work done can also be measured in newton-metres (Nm).

1 J = 1 Nm

It is important not to confuse newton-metres (a unit of work done) with Newton meters (calibrated spring balances used to measure weights).

Example

A doctor weighs 600 N. A lift moves her 40 m to the top floor of a hospital. Calculate the work done on the doctor by the lift.

work done = force × distance

work done = 600 N × 40 m

work done = 24,000 J (or 24 kJ)

Question

In a scrum, a rugby team pushes the other team backwards 5 m using a force of 1,000 N. Calculate the work done moving the other team.

Show answer

work done = force × distance

work done = 1,000 N × 5 m

work done = 5,000 J (or 5 kJ)

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More guides on this topic

  • Scalar and vector quantities - OCR Gateway
  • Motion - OCR Gateway
  • Newton's laws - OCR Gateway
  • Forces and elasticity - OCR Gateway
  • Mass, weight and gravitational field strength - OCR Gateway

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