Force and Motion II: Paper 2 Answering Guide (Form 5 SPM Physics)

Paper 2 at a glance

• Paper 2 carries 100 marks in total

"Define" items from this chapter

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

• Free body diagram, A diagram that shows all the forces acting on a single object, drawn as arrows from the object.
• Inclined plane, A flat surface set at an angle to the horizontal, on which an object's weight can be resolved into components along and perpendicular to the surface.
• Elasticity, The property of a material that allows it to return to its original shape and size after the force deforming it is removed.
• Hooke's law, Within the elastic limit, the extension of a spring is directly proportional to the force applied to it.
• Spring constant, The force needed to produce unit extension in a spring, a measure of its stiffness; measured in newtons per metre (N m⁻¹).
• Elastic limit, The maximum force or extension beyond which a spring or material no longer returns to its original length.

"Explain" items from this chapter

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

• Why a ladder slips on a smooth floor, A leaning ladder stays put only when friction at the floor balances the outward push at the base. On a smooth floor there is too little friction, so the balance breaks and the ladder slides.
• How a spring balance measures weight, A spring stretches in proportion to the force pulling on it. A spring balance reads weight because the extension of its spring is directly linked to the load, following Hooke's law.
• Why a tightrope can never be perfectly horizontal, The person's weight must be balanced by the upward parts of the rope's tension. The flatter the rope, the smaller that upward part, so a truly horizontal rope would need an impossible tension.

"Calculate" items from this chapter

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

• Fₓ = F cos θ, Horizontal component of a force, Fₓ = horizontal component of force (N); F = force (N); θ = angle to the horizontal (°) · Use cos for the component adjacent to the angle (usually horizontal). Measure θ from the horizontal.
• F_y = F sin θ, Vertical component of a force, F_y = vertical component of force (N); F = force (N); θ = angle to the horizontal (°) · Use sin for the component opposite the angle (usually vertical). Measure θ from the horizontal.
• F = kx, Hooke's law, F = force (N); k = spring (force) constant (N m⁻¹); x = extension (m) · x is the extension (change in length), not the total length. Valid only up to the elastic limit.
• E = ½Fx = ½kx², Elastic potential energy, E = elastic potential energy (J); F = force (N); x = extension (m); k = spring (force) constant (N m⁻¹) · Square the extension in ½kx². x is the extension, not the total length. Valid within the elastic limit.

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 4 content standards of Force and Motion II 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.

• 1.1 Resultant Force
• 1.2 Resolution of Forces
• 1.3 Forces in Equilibrium
• 1.4 Elasticity

A three-step answer routine

1. Underline the command word and the quantity asked for.
2. Write the principle or formula before any numbers.
3. Close with the unit, the direction (if a vector) and a one-line conclusion.

More Force and Motion II resources

• Chapter overview: Force and Motion II
• 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)