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Work, Energy and Power

Work done and conservation of energy

  • 2 things to know
  • Papers 1 and 3

Overview

Recall questions on work done and its unit, W = Fx cos θ and calculations with it, the principle of conservation of energy, forms of energy and how energy transfer relates to work done.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

Define work done, state its SI unit and how it is defined in base units, and state what θ represents in W = Fx cos θ.

Key term

What is the definition of work done in physics?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the definition of work done in physics?

    Model answer

    Work done is the energy transferred when a force moves an object through a distance in the direction of the force.

  2. 2

    What is the SI unit of work done, and how is it defined in base units?

    Model answer

    The SI unit of work done is the joule (J), where 1 joule equals 1 newton metre, which is 1 kg m² s⁻² in base units.

  3. 3

    State the equation used to calculate work done when a force acts at an angle to the displacement.

    Model answer

    W = Fx cos θ, where F is the force, x is the displacement, and θ is the angle between the force and displacement vectors.

  4. 4

    In the equation W = Fx cos θ, what does the angle θ represent?

    Model answer

    θ is the angle between the force vector and the displacement vector.

  5. 5

    Why is the cosine function used when calculating work done by a force at an angle?

    Model answer

    The cosine function gives the component of the force acting in the direction of the displacement, since only this component does work.

  6. 6

    Calculate the work done when force = 54 N, displacement = 88.9 m, angle = 38°.

    Model answer

    Work done = 54 × 88.9 × cos 38° = 3780 J.

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