Skip to main content
Next exam on November 14 – 15, 2026:
All concepts

Conservation of Momentum

动量守恒定律

Testing whether momentum is conserved, applying the conservation law to collisions, and the characteristics of a perfectly inelastic collision.

1 real-exam question · 1 sitting7 in mock papers9 practice

Formulas

  • Conservation of momentum

    Law
    m1v1+m2v2=m1v1′+m2v2′m_1v_1+m_2v_2=m_1v_1'+m_2v_2'

    Applies when：No external force, or their vector sum is zero (a good approximation in collisions)

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

  1. CSCA Physics December 2025 Past Paper
    A small ball with a mass of 20 kg collides with a stationary cart on a smooth horizontal surface at a speed of 6 m/s6 \mathrm {~m} / \mathrm { s }. Given that the cart has a mass of 40 kg , the combined speed of the ball and cart after the collision is ( ).
    • A．2 m/s2 \mathrm {~m} / \mathrm { s }
    • B．3 m/s3 \mathrm {~m} / \mathrm { s }
    • C．4 m/s4 \mathrm {~m} / \mathrm { s }
    • D．6 m/s6 \mathrm {~m} / \mathrm { s }
    Show answer & solution

    Answer: A

    1 Perfectly inelastic collision (stick together): conserve momentum. 2 v=(m1v1+m2v2)/(m1+m2)=(20×6+40×0)/60=2 m/s\mathrm { v } = ( \mathrm { m } 1 \mathrm { v } 1 + \mathrm { m } 2 \mathrm { v } 2 ) / ( \mathrm { m } 1 + \mathrm { m } 2 ) = \left( 20 \times 6 + 40 \times 0 \right) / 60 = 2 \mathrm {~m} / \mathrm { s }.
    See it in the full CSCA Physics December 2025 Past Paper

Real-exam evidence

Recorded past-paper appearances are listed below; online verification is labelled separately.

1 question across 1 sitting1 of 1 sittings available to verify free online

7 questions across 3 mock papers — our own papers, so a coverage signal rather than real-exam evidence

9 related practice questions availablePractise free: Momentum and Impulse

Sitting evidence comes from the CSCA past papers on record; questions whose original paper is missing are excluded, and sprint papers are deliberately not counted.

Related concepts

Impulse and the Impulse–Momentum Theorem