Physics Exam Traps
Short guides for the errors that cost marks. Each page shows a wrong answer, the fix, and a calculator to verify the number.
Mass vs Weight Mistakes That Cost Marks
Fix the most common mass vs weight errors: kg as newtons, W in F = ma, g = 9.8 vs 10, normal force on ramps, and Moon g. Wrong → right examples plus free calculators.
SUVAT Sign Mistakes That Flip Your Answer
Fix common SUVAT sign traps: calling all slowing “negative a,” mixing distance with displacement, dropping signs in v² = u² + 2as, and wrong free-fall directions.
F = ma Mistakes: Net Force vs Weight
Stop using weight as net force, forgetting friction opposite motion, mixing kg with N, and applying F = ma to a single force when several act.
Density Unit Mistakes (g/cm³ vs kg/m³)
Fix density traps: mixing grams with m³, treating liters as m³, using object density in Fb = ρVg, and forgetting 1 g/cm³ = 1000 kg/m³.
Work vs Power Mistakes (Joules vs Watts)
Fix work vs power traps: calling watts “work,” leaving time in minutes, using P = Fv when force is not along motion, and mixing mechanical power with P = VI.