Tian2
The Tian2 Study Library AP Edition · Tian2 Editorial Bureau
Volume I · MMXXVI AP Physics C: Mechanics
Library› AP Physics C: Mechanics› Unit 4: Linear Momentum
⁂   AP Physics C: Mechanics · Unit 4

4. Linear Momentum

10–20% of the AP exam. 8 key topics. 4 common errors analyzed.

10–20% exam weight

Unit 4: Linear Momentum

Unit 4 (Linear Momentum) 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. Linear momentum (p = mv)
  2. Impulse and the impulse-momentum theorem: J = ∫F dt = Δp
  3. Conservation of linear momentum
  4. Elastic collisions (kinetic energy conserved)
  5. Inelastic and perfectly inelastic collisions
  6. Two-dimensional collision analysis
  7. Center of mass position and velocity for discrete and continuous mass distributions
  8. Center of mass integrals for uniform objects

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

Applying conservation of momentum without first checking whether net external force is zero — using momentum conservation in problems where a significant external impulse acts during the event

Common error

In 2D collisions, treating momentum as a scalar and summing magnitudes rather than resolving into x- and y-components and conserving each independently

Common error

Confusing impulse with force: writing J = F (omitting the time integral) or treating average force as identical to the net force at a single instant

Common error

Center-of-mass integration errors: setting up ∫x dm with the wrong expression for dm (e.g., using a 1D linear density for a 2D object), or evaluating the integral without dividing by total mass M

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?
← Work, Energy, and PowerTorque and Rotational Dynamics →
← Back to AP Physics C: Mechanics
Our worked solutions and practice questions are original instructional content created by Tian2 AP. They are aligned to the concepts and skills described in College Board’s Course and Exam Description and are not reproductions of, or affiliated with, College Board’s official materials.