Physics
What you must know
Mechanics dominates: kinematics equations, Newton's three laws, work, energy, power, momentum, and circular motion. Then fluids (pressure, buoyancy), heat (specific heat, latent heat), electricity (Ohm's law, series and parallel circuits, power), and basic waves and optics (reflection, refraction, lenses). Dimensional reasoning and unit consistency are exam favourites.
Traps that appear
- Units: convert centimetres to metres and grams to kilograms before substituting.
- Series vs parallel: series adds resistances; parallel adds reciprocals, so total resistance is smaller than any single branch.
- Sign conventions: acceleration due to gravity is negative if upward is positive.
- Confusing mass and weight: weight is (mg), measured in newtons.
- Energy conservation: friction converts mechanical energy to heat, so the final speed is lower than the frictionless case.
Worked example
A 2 kg block slides down a frictionless 5 m ramp inclined at 30°. Height dropped is (5\sin30°=2.5) m. Using (mgh=\tfrac12mv^2), mass cancels: (v=\sqrt{2gh}=\sqrt{2\cdot9.8\cdot2.5}\approx7) m/s. Note that the answer is independent of mass.
Rule of thumb
Write down the knowns with units, identify the unknown, and pick the equation that links them. If units of the result are wrong, the method is wrong.