Physics
Core concepts
Mechanics dominates: kinematics (v = u + at, s = ut + ½at², v² = u² + 2as), Newton's laws, work, energy and power, plus basic statics and pressure. You should also handle simple electric circuits (Ohm's law, series/parallel), density, and the distinction between scalar and vector quantities.
Common traps
- Forgetting to convert km/h to m/s (divide by 3.6).
- Sign conventions: choose a positive direction and keep it throughout.
- Confusing mass and weight (W = mg).
- Adding resistors in parallel: use reciprocals, not direct sums.
- Free-fall: g ≈ 9.8 m/s² downward; velocity at the top of a throw is zero, not acceleration.
Worked example
A car accelerates uniformly from rest to 20 m/s in 8 s. Acceleration a = (20 − 0)/8 = 2.5 m/s². Distance s = ½at² = ½ × 2.5 × 64 = 80 m. Alternatively s = (u+v)t/2 = (0+20)×8/2 = 80 m.
Rule of thumb
List knowns and unknowns with units, choose the equation containing exactly one unknown, and check dimensional consistency before calculating.