Unit Overview
Work, energy and power
CIE A-Level PhysicsΒ· 5 min read π n/a
1. Unit at a glance
This unit follows a logical learning arc that builds on your prior knowledge of forces and motion. We start by defining work, the measure of energy transferred by a force, then move to classifying the two most common forms of mechanical energy: gravitational potential energy and kinetic energy. Next we cover the overarching principle of conservation of energy that governs all physical processes, before ending with rate of energy transfer (power) and efficiency of energy use.
Every concept in this unit builds on the previous one, so we recommend completing the sub-topics in the order listed below.
Sub-topics in this unit:
Work done by a force
Learn the definition of work and calculate work done by constant forces at any angle to displacement.
β β β± 10 min
Gravitational potential energy and kinetic energy
Derive and apply formulas for gravitational potential energy and kinetic energy for moving objects.
β β β± 12 min
Conservation of energy
Apply the principle of conservation of energy to solve problems involving energy transfer.
β β β β± 15 min
Power
Learn the definition of power and calculate the rate of energy transfer for mechanical systems.
β β β± 8 min
Energy efficiency
Calculate the efficiency of energy transfers and explain why energy is lost in real processes.
β β β± 10 min
2. Common Pitfalls
Wrong move:
Forgetting to include the angle between force and displacement when calculating work.
Why:
The simplified formula only works when force is parallel to displacement. For other angles, work is smaller than this value.
Correct move:
Always use the full formula where is the angle between force and displacement.
Wrong move:
Assuming total kinetic energy stays constant when applying conservation of energy.
Why:
Conservation of energy says total energy is constant, not that any single form of energy is constant.
Correct move:
Always account for all forms of energy (potential, heat, sound, etc.) when setting up your energy balance equation.
3. Quick Reference Cheatsheet
Concept | Key Formula / Relationship |
|---|---|
Work done by constant force | |
Kinetic energy | |
Change in gravitational potential energy (near surface) | |
Conservation of energy | Total initial energy = Total final energy |
Power | (for constant parallel force) |
Energy efficiency |
What's Next
Begin your study of this unit with the first sub-topic on work done by a force, which lays the foundation for all other energy concepts covered here. Once you complete all sub-topics in this unit, move on to the next unit on momentum, which continues building your core mechanics knowledge for CIE A-Level Physics.