Physics
The JCE Physics domain samples the junior secondary syllabus: measurement and units, motion and forces, energy, heat, waves and sound, light, electricity and magnetism. Questions reward correct SI units, formula recall with the substitution shown, and interpretation of simple graphs and circuit diagrams. Structured calculations carry a large share of the marks, and credit is given for the equation, the substituted values, the answer and its unit - not the answer alone.
Core rules and concepts
- Work in SI base units: metre (m), kilogram (kg), second (s), ampere (A), kelvin (K). Convert grams to kg and centimetres to m before calculating.
- Average speed = total distance ÷ total time; acceleration = change in velocity ÷ time taken.
- For uniform acceleration use v = u + at, s = ut + ½at² and v² = u² + 2as. On a velocity–time graph, gradient is acceleration and area under the line is distance.
- Newton's laws: balanced forces give zero acceleration; resultant force F = ma; every action has an equal and opposite reaction acting on a different body.
- Ohm's law V = IR applies to ohmic conductors at constant temperature. Series resistances add; in parallel 1/R = 1/R₁ + 1/R₂.
- Energy is conserved: gravitational potential energy mgh transfers to kinetic energy ½mv² when friction is ignored.
Worked example
A car accelerates uniformly from 4 m/s to 16 m/s in 6 s. Find its acceleration and the distance travelled.
a = (v − u)/t = (16 − 4)/6 = 2 m/s². s = ut + ½at² = (4 × 6) + (0.5 × 2 × 36) = 24 + 36 = 60 m. Check using average velocity: ((4 + 16)/2) × 6 = 60 m. Both routes agree, so the answer is 60 m.
Traps that cost marks
- Mixing units: 250 g must become 0.25 kg before F = ma is used.
- Ignoring direction: a braking body has negative acceleration, so substitute a with the correct sign.
- Quoting a numerical answer with no unit or with the wrong unit (N versus kg).
- Confusing mass in kilograms with weight in newtons, where w = mg and g ≈ 10 N/kg.