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Volume I · MMXXVI AP Physics C: Mechanics
Library› AP Physics C: Mechanics› Unit 3: Work, Energy, and Power
⁂   AP Physics C: Mechanics · Unit 3

3. Work, Energy, and Power

15–25% of the AP exam. 8 key topics. 4 common errors analyzed.

15–25% exam weight

Unit 3: Work, Energy, and Power

Unit 3 (Work, Energy, and Power) is part of the calculus-based AP Physics C: Mechanics curriculum. Variable-force problems and differential equations require calculus setup; show your integral expression before evaluating.

Key topics in this unit

  1. Translational kinetic energy
  2. Work done by variable forces: W = ∫F·dx
  3. Work-energy theorem
  4. Conservative vs. non-conservative forces
  5. Potential energy functions derived from force: U = -∫F dx
  6. Conservation of mechanical energy
  7. Energy dissipation by non-conservative forces
  8. Power: P = dW/dt = F·v

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Using W = Fd (constant-force formula) instead of W = ∫F(x) dx when force varies with position, causing incorrect work calculations in spring or variable-force problems

Common error

Sign errors on potential energy change: confusing ΔU = -W_conservative with W_by_gravity, particularly when objects move both up and down within a single problem

Common error

Forgetting to include work done by non-conservative forces (friction, applied forces) in energy conservation equations, treating all problems as if mechanical energy is always conserved

Common error

Conflating instantaneous power (P = Fv) with average power (P = W/Δt), or omitting the dot product angle factor when force and velocity are not parallel

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
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