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Next exam on November 14 – 15, 2026:
All concepts

Gravitation and Satellites

万有引力与航天

The law of universal gravitation and its range of validity, solving orbital motion by equating gravity to the centripetal force, and computing surface gravity and cosmic velocities.

4 real-exam questions · 4 sittings6 in mock papers6 practice

Formulas

  • Law of universal gravitation

    Law
    F=Gm1m2r2F=G\frac{m_1m_2}{r^2}

    Applies when：Valid for point masses or uniform spheres; r is the centre-to-centre distance

  • Surface gravitational acceleration

    Formula
    g=GMR2g=\frac{GM}{R^2}

    Applies when：Rotation neglected; M and R are the planet's mass and radius

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
    The gravitational force acting on an object on Mars is 1/31 / 3 of the gravitational force acting on it on Earth. Therefore, the gravitational force acting on an object of mass m=4.8 kg\mathrm { m } = 4.8 \mathrm {~kg} on Mars is ( ), ( g=10m/s2\mathrm { g } = 10 \mathrm { m } / \mathrm { s } ^ { 2 } )
    • A．144 N
    • B．24 N
    • C．48 N
    • D．16 N
    Show answer & solution

    Answer: D

    1 Mars weight is one-third of Earth weight: W=(1/3)mg\mathrm { W } = ( 1 / 3 ) \mathrm { mg }. 2 Compute: W=(1/3)×4.8 kg×10 m/s2=16 N\mathrm { W } = ( 1 / 3 ) \times 4.8 \mathrm {~kg} \times 10 \mathrm {~m} / \mathrm { s } ^ { 2 } = 16 \mathrm {~N}.
    See it in the full CSCA Physics December 2025 Past Paper
  2. CSCA Physics March 2026 Past Paper
    An object weighs 30 N on the Moon. Given that the Moon's gravitational acceleration is 1/61 / 6 that of Earth's, the object's weight on Earth is
    • A．5 N
    • B．30 N
    • C．180 N
    • D．300 N
    Show answer & solution

    Answer: C

    Mass does not change with location. On the Moon: WMoon=mgMoon=30 NW_{\mathrm{Moon}} = m g_{\mathrm{Moon}} = 30 \mathrm {~N}. Since gMoon=gEarth/6g_{\mathrm{Moon}} = g_{\mathrm{Earth}}/6, WEarth=6×WMoon=6×30=180 NW_{\mathrm{Earth}} = 6 \times W_{\mathrm{Moon}} = 6 \times 30 = 180 \mathrm {~N}. A divides by 6; B fails to convert; D has an extra factor. Answer: C.
    Take the full CSCA Physics March 2026 Past Paper — timed & graded
  3. CSCA Physics April 2026 Past Paper
    An object's weight on the Moon is approximately 16\frac { 1 } { 6 } of its weight on Earth. If the object's mass is m=6 kgm = 6 \mathrm {~kg} and the gravitational acceleration on Earth is g=10 m/s2g = 10 \mathrm {~m} / \mathrm { s } ^ { 2 }, its weight on the Moon is
    • A．36 N
    • B．10 N
    • C．60 N
    • D．6 N
    Show answer & solution

    Answer: B

    On Earth, weight G=mg=6×10=60 NG = m g = 6 \times 10 = 60 \mathrm {~N}. On the Moon, weight =16×60== \frac { 1 } { 6 } \times 60 = 10 N .
    Take the full CSCA Physics April 2026 Past Paper — timed & graded

Real-exam evidence

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

4 questions across 4 sittings1 of 4 sittings available to verify free online
  • CSCA Physics April 2026 Past Paper1 questionreading page not yet public
  • CSCA Physics March 2026 Past Paper1 questionreading page not yet public
  • CSCA Physics January 2026 Past Paper1 questionreading page not yet public
  • CSCA Physics December 2025 Past Paper1 questionView question 2 and answer free (full paper)

6 questions across 6 mock papers — our own papers, so a coverage signal rather than real-exam evidence

6 related practice questions availablePractise free: Circular Motion and Universal Gravitation

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.

Glossary

acceleration

Related concepts

Forces and EquilibriumNewton's Laws of MotionCircular Motion