SOLUTIONS — SAMPLE PAPER 3

Section A

1. a
2. b
3. b
4. b
5. c
6. a
7. b
8. b
9. a
10. b

Section B

11. Air resistance may be ignored when it is small compared with the effect being studied. This simplifies the model and allows the main effect, such as gravity, to be understood more clearly.

12. A numerical value without a unit may be ambiguous. Units tell us what quantity has been measured and allow results to be compared correctly.

13. Evidence-based means supported by observations, measurements, experiments or other reliable data rather than by unsupported belief.

14. Predicting the likelihood of rain using measurements of humidity, pressure, temperature and wind is one example.

15. Estimation gives an approximate expected range. If a calculated result is extremely different from that range, it may indicate an error in reasoning, units or calculation.

Section C

16. A model does not need to reproduce every detail of reality. It only needs to include the features relevant to the question. This makes a complex system easier to study. A moving car, for example, may be treated as a point when only its motion is being considered.

17. Real-world systems do not follow school-subject boundaries. For example, understanding a surgical mask may require physics to study particles and airflow, chemistry to understand polymer fibres, biology to understand microorganisms, and mathematics to analyse data.

18. Measurement turns observations into quantitative information. Repeated and careful measurements provide evidence that can be compared, analysed and used to test scientific explanations and predictions.

19. No. Weather depends on many changing factors and scientific forecasts have limits. A prediction that does not match observation should lead scientists to examine the measurements, model and assumptions. This process can improve future predictions.

Section D

20.

a) Estimated water use:

800 × 1 L = 800 L

b) The assumption of 1 L per student is only an average estimate. Students may consume different amounts.

c) Weather, physical activity, age, availability of water and individual habits could change the actual value.

21.

a) The student should collect repeated measurements of plant growth under similar conditions and compare plants placed near and away from the window.

b) Water supplied, soil type, plant species, pot size or starting size should be kept similar.

c) One observation cannot establish a reliable relationship because other factors may have caused the difference. Repeated observations and controlled comparisons provide stronger evidence.

Section E

22. First, a scientist observes a phenomenon and asks a question about it. Relevant quantities and conditions are identified. Evidence from previous observations or experiments is considered. A model or explanation may then be used to make a prediction.

For example, if dark clouds are observed, instead of simply predicting rain, a scientist may consider humidity, temperature, pressure, wind and previous weather patterns. The prediction should be testable through later observation.

If the prediction agrees with observations, confidence in the model increases. If it does not, the assumptions or model may need revision.

23. Standard units provide a common reference for measurement. Without them, the same numerical value could represent different quantities.

For example, kilograms and pounds are different units of mass. Confusing them can produce serious errors in calculations and real-world applications.

Using internationally agreed units makes scientific measurements easier to compare and reduces errors caused by unnecessary conversions.