Physics: Mechanics, Electricity and Practical Reasoning
Core concepts to master
Build fluency in kinematics (displacement, velocity, acceleration, equations of uniformly accelerated motion), Newton's three laws, momentum and its conservation, work–energy and power, circular motion, and gravitation. In electricity, know Ohm's law, series and parallel resistance, electrical power, and the qualitative behaviour of magnetic fields around currents. Waves and optics reward familiarity with reflection, refraction, Snell's law, and the lens formula. Modern physics questions usually test photoelectric thresholds, atomic energy levels, and half-life arithmetic rather than deep derivation.
Traps examiners set
- Confusing speed with velocity and forgetting direction in vector problems.
- Using g = 10 m/s² when the paper specifies 9.8, or mixing units (cm with m).
- Applying conservation of momentum to systems with external friction without noticing.
- In parallel circuits, assuming current splits equally rather than inversely with resistance.
- Sign conventions in lens and mirror formulas.
Rule of thumb
Write the known quantities with units first, convert everything to SI, then choose the equation containing exactly one unknown. Dimensional checking catches most slips.
Worked example
A 2 kg block slides from rest down a frictionless 5 m incline of height 3 m. Find its speed at the bottom.
Energy conservation: mgh = ½mv², so v = √(2gh) = √(2 × 9.8 × 3) ≈ √58.8 ≈ 7.7 m/s. The incline length is a distractor unless time is asked; if it were, use a = g sin θ with sin θ = 3/5.
Practice habit
Sketch every setup, label forces, and check whether the question asks for magnitude only or direction as well.