Work, Energy & Power — A-Level Physics Revision

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What is Work, Energy & Power?

This topic connects the concepts of force and motion with energy. Work is defined as the energy transferred when a force causes displacement, and power is the rate at which work is done or energy is transferred. You will learn to calculate work done, kinetic energy, and gravitational potential energy, and apply the fundamental principle of conservation of energy to solve problems involving energy transformations.

Board notes: A core mechanics topic for all A-Level boards (AQA, Edexcel, OCR). All boards expect proficiency in calculations involving work, kinetic energy, potential energy, and power. The application of the conservation of energy principle in various contexts, including those with resistive forces, is a common examination focus.

Worked example

Common mistakes

• 1Forgetting that the displacement in the work done equation (W = Fx cosθ) must be in the direction of the force. If the force and displacement are perpendicular, no work is done.
• 2Confusing the principle of conservation of energy with the conservation of mechanical energy. Total energy is always conserved, but mechanical energy (KE + PE) is only conserved in the absence of non-conservative forces like friction or air resistance.
• 3Using inconsistent units in calculations, for example, using mass in grams instead of kilograms, or time in minutes instead of seconds when calculating power.

Work, Energy & Power exam questions

Exam-style questions for Work, Energy & Power with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is the work-energy principle?

  The work-energy principle states that the net work done on an object is equal to the change in its kinetic energy. This provides a direct link between the forces acting on an object and its change in speed.

• What is efficiency in the context of energy and power?

  Efficiency is a measure of how effectively energy is transferred or converted. It is calculated as the ratio of useful energy (or power) output to the total energy (or power) input, often expressed as a percentage.