Questions
1. Calculate: A force F = 50 N acts at θ = 30° to the horizontal. Find the unknown using Fₓ = F cos θ.
Fₓ = F cos θ = 50 × cos 30° = 50 × 0.866 = 43.3 N.
2. Calculate: A force F = 50 N acts at θ = 30° to the horizontal. Find the unknown using F_y = F sin θ.
F_y = F sin θ = 50 × sin 30° = 50 × 0.5 = 25 N.
3. Calculate: A spring of constant k = 200 N m⁻¹ is stretched by x = 0.05 m. Find the unknown using F = kx.
F = kx = 200 × 0.05 = 10 N.
4. Calculate: A spring with k = 200 N m⁻¹ is stretched by x = 0.05 m. Find the unknown using E = ½Fx = ½kx².
E = ½kx² = ½ × 200 × 0.05² = ½ × 200 × 0.0025 = 0.25 J.
5. State the manipulated, responding and constant variables for: To investigate the relationship between the stretching force and the extension of a spring and to determine the spring constant.
Manipulated: Stretching force, F (the weight of the load). Responding: Extension of the spring, x. Constant: The same spring.
6. Explain: 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.
7. Explain: 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.
8. Explain: 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.
9. Define elasticity.
The property of a material that allows it to return to its original shape and size after the force deforming it is removed.
10. Define hooke's law.
Within the elastic limit, the extension of a spring is directly proportional to the force applied to it.
11. Define 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).
12. Define elastic limit.
The maximum force or extension beyond which a spring or material no longer returns to its original length.
13. Define limit of proportionality.
The point up to which the extension of a spring stays directly proportional to the applied force.
14. Define elastic potential energy.
The energy stored in a spring or elastic object when it is stretched or compressed.
Marking yourself
- Calculation: formula written, values substituted with units, final answer with unit and sensible significant figures.
- Variables: manipulated = what you change; responding = what you measure; constant = what you keep the same.
- Definition: one sentence, correct physical quantity, correct unit.
Exam tip
More Force and Motion II resources
- Chapter overview: Force and Motion II
- Revision Notes
- Common Mistakes
- Paper 2 Answering Guide
- 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)