Physics
Physics questions test conceptual understanding and short numericals from motion, force, work and energy, pressure, heat, waves and sound, light, electricity, and magnetism. The PN Cadet paper favours definitions, units, laws, and one-step calculations.
Core rules
- Speed is scalar; velocity is vector. Acceleration = change in velocity ÷ time.
- Newton’s second law: F = ma. Weight = mg, so mass is not weight.
- Work = force × distance in the direction of force; power = work ÷ time; kinetic energy = ½mv².
- Pressure = force ÷ area; liquid pressure increases with depth.
- Ohm’s law: V = IR. In series, current is common; in parallel, voltage is common.
- Angle of incidence equals angle of reflection, measured from the normal.
Worked example
A car starts from rest and accelerates at 2 m/s² for 5 s. Final velocity v = u + at = 0 + 2×5 = 10 m/s. Distance s = ut + ½at² = 0 + ½×2×25 = 25 m. If you used s = vt, you would wrongly get 50 m because velocity was not constant; the average velocity here is (0 + 10)/2 = 5 m/s, and 5×5 = 25 m.
Traps
Do not treat weight as mass or use g unless the question involves weight. Convert cm to m and grams to kg. In circuits, do not add parallel resistances directly; use 1/R = 1/R₁ + 1/R₂. In sound and light, check whether the question asks for frequency, wavelength, or speed. A vector answer needs direction, not just magnitude.