Physics
Physics questions test school-level mechanics, heat, waves, electricity, magnetism and optics, mixing short numericals with conceptual checks. Formula recall matters, but most marks are lost to units and signs rather than to algebra.
Core rules and concepts
- Kinematics: v = u + at, s = ut + ½at², v² = u² + 2as.
- Newton’s three laws; momentum p = mv and its conservation; friction and moments (moment = force × perpendicular distance).
- Work, power and energy: W = Fs, P = W/t, KE = ½mv², PE = mgh; energy is conserved, never created.
- Pressure, Archimedes’ principle, floatation and Bernoulli’s principle for flowing fluids.
- Heat: Q = mcΔθ and Q = mL; expansion of solids and liquids.
- Waves: v = fλ; sound travels at about 330–340 m/s in air; echo timing uses twice the distance.
- Electricity: V = IR, P = VI; series and parallel combinations; magnetic effect of a current.
- Light: reflection, refraction, Snell’s law, focal length of lenses and mirrors.
Worked example
A car starts from rest and accelerates at 2 m/s² for 5 s. Find its speed and distance. Using v = u + at with u = 0: v = 2 × 5 = 10 m/s. Using s = ut + ½at²: s = 0 + ½ × 2 × 25 = 25 m. A check with average speed, (0 + 10)/2 × 5 s = 25 m, confirms the answer.
Traps that cost marks
- Mixing grams with kilograms, or centimetres with metres, before substituting.
- Treating mass and weight as the same quantity (weight = mg).
- Expecting two resistors in parallel to exceed the smallest of them - the total is always smaller.
- Forgetting that an echo travels to the reflector and back.
Write the formula, substitute with units, then state the unit in the final answer.