Quantities and units in mechanics (AS Unit 2: Applied Mathematics A) — WJEC A-Level Mathematics
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Quantities and units in mechanics (AS Unit 2: Applied Mathematics A) explained
The International System of Units (SI) establishes base physical quantities from which all mechanical metrics derive.
Read the full explanation
The fundamental mechanical base quantities are length, measured in metres (m); time, measured in seconds (s); and mass, measured in kilograms (kg). Candidates must operate fluently with metric prefixes—converting kilometres to metres (1 km = 1000 m), grams to kilograms (1000 g = 1 kg), and minutes or hours to seconds (1 h = 3600 s). In mechanics problems, dimensional consistency across equations is vital: substituting unstandardised units like grams or kilometres per hour without prior conversion to SI base units introduces immediate fatal calculation errors.
Your focus
- Identify and use SI base units for length (m), time (s), and mass (kg) in mechanical models.
- Convert measurements with metric prefixes and temporal units into standard SI base values.
- Verify dimensional consistency across algebraic and numerical equations in mechanics.
Quantities and units in mechanics (AS Unit 2: Applied Mathematics A) exam tips
Marking Points
- converting non-standard inputs (such as grams to kilograms or minutes to seconds) into base SI units
- maintaining dimensional consistency across mechanical formulas
- stating final numerical quantities with correct SI base units
Examiner Tips
- 💡Always scan problem text for non-standard units (e.g. g, km, minutes) and convert immediately to kg, m, and s.
- 💡Include explicit units in your final answer line to secure available accuracy marks.
Common Mistakes
- substituting mass in grams instead of converting to kilograms in dynamic equations
- using time in minutes rather than seconds when calculating displacement or acceleration