Equation Practice and Calculations
At least 20% of your marks depend on maths
Why This Matters
AQA Science papers allocate at least 20% of marks to mathematical skills. In Physics, this can rise to 40%. You need to recall equations (some are given on the equation sheet, others must be memorised), rearrange them, substitute values with correct units, and present answers to an appropriate number of significant figures. In Chemistry, you’ll calculate relative formula masses, moles, concentrations, and atom economy. In Biology, maths questions involve magnification, percentages, and data analysis. Students who don’t practise calculations lose easy marks.
Step-by-Step Method
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1
Learn which equations must be memorised — AQA provides an equation sheet in the exam, but not all equations are on it. For Higher tier Physics, you must memorise equations like F = ma, E = mcΔθ, and V = IR. Make flashcards for the “recall” equations and drill them until automatic.
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2
Practise rearranging — Use the formula triangle method or algebraic rearranging. For every equation, practise making each variable the subject. For example: speed = distance ÷ time can become distance = speed × time, or time = distance ÷ speed.
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3
Convert units before substituting — Always convert to SI units: km to m, g to kg, mA to A, kJ to J, cm² to m². Write the conversion next to the value before substituting into the equation.
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Show every step of working — Write the equation, substitute values with units, calculate, and state the unit of the answer. Even if the final number is wrong, you can earn marks for correct method.
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Check significant figures and standard form — Give answers to an appropriate number of significant figures (usually 2 or 3 s.f.) and use standard form for very large or very small numbers (e.g. 3.0 × 10⁸ m/s).
When and How Often
Spend 20–25 minutes per session. Start with equation recall (flashcards or brain dump), then work through 5–8 calculation questions. Practise at least 3 times per week — maths skills fade quickly without regular use.
Physics — Must Recall (not on equation sheet)
| Quantity | Equation |
|---|---|
| Speed | v = s ÷ t |
| Acceleration | a = Δv ÷ t |
| Newton’s Second Law | F = m × a |
| Weight | W = m × g |
| Work done | W = F × s |
| Kinetic energy | KE = ½ × m × v² |
| GPE | GPE = m × g × h |
| Power | P = E ÷ t |
| Efficiency | Efficiency = useful output ÷ total input |
| Charge | Q = I × t |
| Potential difference | V = I × R |
| Power (electrical) | P = V × I |
| Energy transferred | E = Q × V |
| Density | ρ = m ÷ V |
| Specific heat capacity | ΔE = m × c × Δθ |
| Wave speed | v = f × λ |
| Pressure | p = F ÷ A |
Chemistry — Key Calculations
- Relative formula mass (Mr) = sum of relative atomic masses
- Moles = mass ÷ Mr
- Concentration (g/dm³) = mass ÷ volume
- Atom economy = (Mr of desired product ÷ Mr of all products) × 100
- Percentage yield = (actual yield ÷ theoretical yield) × 100
Biology — Key Calculations
- Magnification = image size ÷ actual size
- Percentage change = (change ÷ original) × 100
- Mean, median, mode, and range from data tables
Question: A 0.5 kg ball is dropped from a height of 12 m. Calculate its speed just before hitting the ground. Assume g = 10 m/s² and no air resistance. [3 marks]
Step 1: GPE lost = m × g × h = 0.5 × 10 × 12 = 60 J
Step 2: KE gained = GPE lost = 60 J (conservation of energy)
Step 3: KE = ½ × m × v² → v² = 2 × KE ÷ m = 2 × 60 ÷ 0.5 = 240 → v = √240 = 15.5 m/s (3 s.f.)
Common Mistakes
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Forgetting unit conversions — Using km instead of m, or g instead of kg, gives answers out by factors of 1000. Always convert first.
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Not showing working — An answer without working earns 0 marks if the number is wrong. Show every step to pick up method marks.
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Missing the unit of the answer — Always state the unit (J, N, m/s, mol). Marks are often lost for missing units.