This set covers controlled conditions, safe measurement improvements, systematic error, alternative conclusions and who handles what for practical work. All data is invented. Write your answer first, then open the working.
Questions run from easier to harder. A mistake log helps you track repeats, and the scientific investigation critic lets you rehearse critiques. Back to the module overview.
Questions
1. A student tests how the mass of a trolley affects the distance it rolls down a ramp. List three conditions that should be kept the same.
Show answer
Ramp angle, ramp surface and release point (also the same trolley wheels). Mass is the independent variable, so it is not controlled. Distance rolled is the dependent variable.
2. Three readings of a length are 14.2 cm, 14.0 cm and 14.4 cm. Find the mean.
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14.2 + 14.0 + 14.4 = 42.6, and 42.6 ÷ 3 = 14.2 cm.
3. A stopwatch reading of 4.0 s has a reaction-time uncertainty of 0.2 s. What percentage is that?
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0.2 ÷ 4.0 × 100 = 5%.
4. Twenty swings of a pendulum take 36.4 s. Find the time for one swing and the percentage uncertainty if the same 0.2 s error applies.
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36.4 ÷ 20 = 1.82 s per swing. 0.2 ÷ 36.4 × 100 = 0.55%, so about 0.55%, much smaller than timing one swing alone.
5. An empty balance shows 0.3 g. A sample then reads 5.8 g. What is the sample’s mass, and what kind of error is this?
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5.8 − 0.3 = 5.5 g. It is a systematic error (a zero error), because every reading is shifted by the same amount.
6. Readings are 9.9 g, 10.0 g and 10.1 g, but the true mass is 12.0 g. Describe the readings using the words precise and accurate.
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Mean = (9.9 + 10.0 + 10.1) ÷ 3 = 30.0 ÷ 3 = 10.0 g. The readings are precise (close to each other) but not accurate (2.0 g below the true value), which suggests a systematic error.
7. Two cups hold 80 °C water at the start. After 10 minutes the covered cup reads 61 °C and the uncovered cup reads 54 °C. State the conclusion and one alternative explanation.
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Drops: covered 80 − 61 = 19 °C, uncovered 80 − 54 = 26 °C. Conclusion: the data are consistent with the lid reducing cooling. Alternative: the cups were different sizes or materials, or sat in different air movement, so something other than the lid explains the difference. Using identical cups in the same place would test this.
8. A student suggests heating a liquid until it boils vigorously to “get a clearer reading”. Say why this is not a suitable improvement and offer a safe one.
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It could be hazardous and is not needed to improve the reading. A safe improvement is to use a thermometer with finer divisions, so the reading uncertainty is smaller.
9. Readings of a temperature rise are 2.1, 2.0, 2.9 and 2.1 °C. Find the mean with all readings and without the odd one. Which is better to report, and what should you say about it?
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All: 9.1 ÷ 4 = 2.275, about 2.3 °C. Without 2.9: 6.2 ÷ 3 = 2.067, about 2.1 °C. Report 2.1 °C and state that 2.9 °C was treated as an anomaly, ideally with a possible reason. Do not delete it silently.
10. A classmate says “my tuition teacher will register me for the practical paper”. Who handles this, and what can the teacher help with?
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Registration, entry and practical arrangements belong to the exam centre. A teacher can help you practise planning, tables, graphs, conclusions and evaluation questions on paper.
If you got these wrong
| Question | Likely error | Go to |
|---|---|---|
| 1, 7 | Missed a changing condition or a rival explanation | controlled conditions, alternative conclusions |
| 3, 4, 8 | Vague or unsafe improvement, percentage slip | measurement improvement |
| 2, 5, 6, 9 | Confused random and systematic error | repeated readings |
| 10 | Mixed up tuition and centre roles | preparation and provision |
If the same row keeps catching you, online one-to-one Combined Science tuition can work on it with your own answers.