Pressure: Paper 2 Answering Guide (Form 5 SPM Physics)

Paper 2 at a glance

• Section B: 2 items worth 20 marks, answer one

"Define" items from this chapter

One precise sentence each; the unit is part of the definition where there is one.

• Pressure, The force acting normally (perpendicularly) on unit area of a surface (pressure = force ÷ area); measured in pascals (Pa).
• Pressure in liquids, The pressure at a point in a liquid, which increases with depth and density (pressure = height × density × gravitational field strength) and acts equally in all directions.
• Atmospheric pressure, The pressure exerted by the weight of the column of air in the atmosphere on the Earth's surface and on objects in it.
• Gas pressure, The pressure produced by the collisions of gas particles with the walls of their container.
• Pascal's principle, Pressure applied to an enclosed fluid is transmitted equally and undiminished throughout the fluid in all directions.
• Hydraulic system, A system that uses Pascal's principle to multiply force by transmitting pressure through an enclosed liquid, as in a hydraulic jack.

"Explain" items from this chapter

Give the physics reason, not a description. Model answers in one breath:

• Why pressure increases with depth, The deeper you go, the more water lies above you, and its weight presses down. So water pressure grows steadily with depth, not with the shape or width of the container.
• How a hydraulic jack lifts a car, Pressure applied to a trapped liquid is passed on equally throughout it. A small force on a small piston creates a pressure that pushes a large piston with a much bigger force.
• Why ships float even though they are heavy, A floating object pushes aside water whose weight equals its own. A steel ship is hollow, so it displaces enough water to support its weight and floats, even though steel itself sinks.
• How an aeroplane wing generates lift, Air moves faster over the curved top of a wing than underneath. Faster-moving air has lower pressure, so the higher pressure below pushes the wing up, giving lift.

"Calculate" items from this chapter

Formula, substitution with units, answer with unit, and the trap examiners set for each one.

• P = F / A, Pressure, P = pressure (Pa); F = force (N); A = area (m²) · Area must be in m² (convert cm²: 1 cm² = 10⁻⁴ m²). Recall that Pa = N m⁻².
• P = hρg, Pressure in a liquid column, P = liquid pressure (Pa); h = depth (m); ρ = density (kg m⁻³); g = gravitational acceleration (m s⁻²) · h is the vertical depth, not the distance along a slope. This is only the liquid pressure, add atmospheric pressure for the total pressure.
• F₁ / A₁ = F₂ / A₂, Pascal's principle, F₁ = force on small piston (N); A₁ = area of small piston (m²); F₂ = force on large piston (N); A₂ = area of large piston (m²) · The force is multiplied in the ratio of the areas. Keep both areas in the same unit.
• Fb = ρVg, Buoyant force (Archimedes' principle), Fb = buoyant force (N); ρ = density of fluid (kg m⁻³); V = volume of fluid displaced (m³); g = gravitational acceleration (m s⁻²) · Use the density of the fluid, not the object. V is the volume of fluid displaced (the submerged volume).

Other command words

• Compare, same feature, both cases, one line each, then the physics that links them.
• Suggest / Modify (Section C), one modification, one reason, tied to a named physics principle; repeat for each aspect the question lists.

Where the marks are in this chapter

The 6 content standards of Pressure can each be asked as a definition, an explanation, a calculation or a diagram. We do not predict which will appear, prepare all of them.

• 2.1 Pressure in Liquids
• 2.2 Atmospheric Pressure
• 2.3 Gas Pressure
• 2.4 Pascal's Principle
• 2.5 Archimedes' Principle
• 2.6 Bernoulli's Principle

A three-step answer routine

1. Decide the answer type first: definition, reason, number or drawing.
2. For numbers, write the rearranged formula on its own line before substituting.
3. Check the magnitude is sensible for the situation before moving on.

More Pressure resources

• Chapter overview: Pressure
• Revision Notes
• Common Mistakes
• Practice Questions
• Paper 3 Guide
• Key Terms
• Calculation practice sets

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)