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Work transfers energy into a spring Terminal motion still transfers energy Maintaining speed requires power Where does a battery’s power go? Power equations must use the component’s operating point Mechanical and electrical power measure the same rate Work, energy and power3.3 Kinematics3.1.1 Motion with non-uniform acceleration3.2.2 Power3.3.3 Resistance4.2.3 Power in circuits4.2.5 Internal resistance4.3.2 Elastic potential energy
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Mechanical and electrical power measure the same rate

OCR A AS Physics · Two ideas, one explanation

A motor transfers electrical energy into mechanical work and other forms. Comparing input and useful output powers gives efficiency.

Pin = VI Puseful = Fv Efficiency = Puseful/Pin

Follow the reasoning

  1. Calculate the electrical input power.
  2. Calculate the useful mechanical output power.
  3. Compare them and account for the remaining transfer rate.
Specification outcomes (5)
  • 3.3.3(a) Define power, the unit watt, and use P = W / t.
  • 3.3.3(b) Use and derive P = Fv from first principles.
  • 3.3.3(c) Calculate efficiency of a mechanical system using percentage efficiency = (useful output energy / total input energy) × 100.
  • 4.2.5(a) Use and apply power equations P = IV, P = I²R, and P = V² / R.
  • 4.2.5(b) Use energy transfer equation W = VIt.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

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