Work, Energy, Power and Efficiency
Tracking energy transfers using work, kinetic and gravitational potential energy, power, efficiency and conservation principles.
How to study A-level Physics
Define the system, represent the physics, select a justified model, calculate transparently, then test the result against units, limits and evidence.
Core concepts
Concept 1
Work is the energy transferred by a force through displacement, using the component parallel to the displacement.
Exam cue: Define the initial and final system states before writing an energy balance.
Concept 2
Energy is conserved across a defined system although it may be dissipated into less useful stores.
Exam cue: Include the angle between force and displacement when required.
Concept 3
Power is the rate of energy transfer and efficiency compares useful output with total input.
Exam cue: Use time consistently when connecting work, power and motion.
Risk pitfalls and guardrails
Calling energy lost when it has been transferred to thermal or other stores.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Using total force rather than the relevant component in work.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Giving efficiency greater than one or 100%.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Memory anchors
Work
Work equals force times displacement in the force direction.
Kinetic Energy
Kinetic energy is one half mass times speed squared.
Gravitational Energy
Near Earth's surface, gravitational potential energy change is mass times field strength times height change.
Power
Power is energy transferred per unit time.
Efficiency
Efficiency is useful output divided by total input using consistent energy or power quantities.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A constant 50 N force moves a box 3.0 m in the force direction. How much work is done?
A 40 N force acts at 60° to a 5.0 m displacement. What work does this force do?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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