Are formulas given in the exam?

No. You must recall SPM Physics formulas.

Is a formula sheet given for these calculations?

No. SPM Physics (4531) provides no formula sheet, recall each formula and write units on every line.

What does the medium band mean?

Mid-level items usually need one rearrangement and a unit conversion.

Can a tutor mark my working?

Yes, in a one-to-one lesson the teacher checks each line and fixes the exact step that loses marks. From RM50/hr, paid trial available.

Pressure Calculations (Medium), SPM Physics

How to approach

These need a rearrangement or two steps, often finding one quantity before the one asked for.

The method

List what is given, with units.
Choose the formula and rearrange for the unknown.
Substitute with units on every line.
Round to the correct significant figures.

Worked examples

Pressure

P = F / A

A force F = 200 N acts over an area A = 0.5 m². P = F / A = 200 / 0.5 = 400 Pa.

Pressure in a liquid column

P = hρg

Find the pressure at depth h = 2.0 m in water (ρ = 1000 kg m⁻³, g = 9.81 m s⁻²). P = hρg = 2.0 × 1000 × 9.81 = 19620 Pa ≈ 1.96 × 10⁴ Pa.

Pascal's principle

F₁ / A₁ = F₂ / A₂

A hydraulic system: F₁ = 20 N on A₁ = 0.01 m² acts on a piston of A₂ = 0.05 m². F₂ = F₁ × A₂ / A₁ = 20 × (0.05 / 0.01) = 100 N.

Buoyant force (Archimedes' principle)

Fb = ρVg

An object displaces V = 2.0 × 10⁻³ m³ of water (ρ = 1000 kg m⁻³, g = 9.81 m s⁻²). Fb = ρVg = 1000 × 2.0 × 10⁻³ × 9.81 = 19.62 N ≈ 19.6 N.

Where marks are lost

Skipping units, rounding too early, and writing only the final answer (which loses method marks in Paper 2).

Practise these

Try each formula above with your own numbers, showing every line. Bring anything you get stuck on to a one-to-one lesson.

Formulas you use for Pressure calculations

These mid-level problems draw on the 4 relationships in Pressure. None is printed in the exam, so recall each and write its symbols with units before substituting:

P = F / A, Pressure
P = hρg, Pressure in a liquid column
F₁ / A₁ = F₂ / A₂, Pascal's principle
Fb = ρVg, Buoyant force (Archimedes' principle)

A worked example, with units on every line

Using F₁ / A₁ = F₂ / A₂ (F₁ = force on small piston (N); A₁ = area of small piston (m²); F₂ = force on large piston (N); A₂ = area of large piston (m²)):

A hydraulic system: F₁ = 20 N on A₁ = 0.01 m² acts on a piston of A₂ = 0.05 m².
F₂ = F₁ × A₂ / A₁ = 20 × (0.05 / 0.01) = 100 N.

Where the marks are, and the common mistakes

In Paper 2, calculation marks are awarded line by line: the formula, the substitution with units, and the final answer with its unit and sensible significant figures. Watch this trap: The force is multiplied in the ratio of the areas.

Keep both areas in the same unit. For mid-level items, expect one rearrangement and a unit conversion.

Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)

Written by the spmphysics.com.my editorial team.· Updated 5 Sept 2026