How to approach
Higher-order questions apply the formula to a described situation and ask you to explain or justify. Structure your answer: state, calculate, then interpret.
The method
- List what is given, with units.
- Choose the formula and rearrange for the unknown.
- Substitute with units on every line.
- Round to the correct significant figures.
Worked examples
Where marks are lost
Practise these
Try each formula above with your own numbers, showing every line. Bring anything you get stuck on to a one-to-one lesson.
Formulas you use for Gravitation calculations
These higher-order (KBAT) problems draw on the 4 relationships in Gravitation. None is printed in the exam, so recall each and write its symbols with units before substituting:
- F = G m₁m₂ / r², Newton's universal law of gravitation
- g = GM / r², Gravitational acceleration (field strength)
- T² ∝ r³ (T²/r³ = constant), Kepler's third law
- v = √(GM / r), Orbital velocity of a satellite
A worked example, with units on every line
Using v = √(GM / r) (v = orbital velocity (m s⁻¹); G = gravitational constant (N m² kg⁻²); M = mass of planet (kg); r = orbital radius (m)):
A satellite orbits Earth (M = 6.0 × 10²⁴ kg) at r = 7.0 × 10⁶ m (G = 6.67 × 10⁻¹¹).
v = √(GM / r) = √((6.67 × 10⁻¹¹ × 6.0 × 10²⁴) / 7.0 × 10⁶) = 7.56 × 10³ m s⁻¹.
Where the marks are, and the common mistakes
In Paper 2, calculation marks are awarded line by line: the formula, the substitution with units, and the final answer with its unit and sensible significant figures. Watch this trap: r is measured from the planet's centre, not the surface.
The orbital speed does not depend on the satellite's own mass. For higher-order (KBAT) items, expect multi-step problems that combine two relationships or ask you to rearrange before substituting.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)