A student investigates how the speed of a trolley changes with the height of the ramp it rolls down. She plans to change the height of one end of the ramp and measure the speed of the trolley at the bottom each time. Describe how the student should make her investigation valid and how she should ensure her results are reliable. Include in your answer what she should do with any anomalous results.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student uses a ramp and a trolley to investigate how the height of a ramp affects the speed of the trolley at the bottom. She measures height in centimetres and speed in metres per second.
Model answer (5 marks)
1. Keep all other variables constant – the mass of the trolley, the length of the ramp and the surface of the ramp must remain unchanged.
2. Repeat each measurement at least three times for each height.
3. Calculate a mean (average) speed from the repeated readings.
4. Identify anomalous results by checking whether a value is significantly different from the other repeated readings.
5. Exclude anomalous results from the calculation of the mean – do not include them when averaging.
2. Repeat each measurement at least three times for each height.
3. Calculate a mean (average) speed from the repeated readings.
4. Identify anomalous results by checking whether a value is significantly different from the other repeated readings.
5. Exclude anomalous results from the calculation of the mean – do not include them when averaging.
Examiner tips
- Use the command word ‘describe’ – give a short list of steps, not a long explanation. Show the order of operations: control variables → repeat → mean → check for outliers → exclude outliers.
Common mistakes
- Failing to keep the mass of the trolley constant. Not repeating measurements or using only one trial. Including anomalous data in the mean calculation.
Mark scheme (5 marks)
- Keep all other variables constant / control variables (e.g. keep the mass of the trolley the same / keep the length of the ramp the same / keep the surface of the ramp the same)
- Repeat each measurement (at each height) at least three times
- Calculate a mean (average) speed from the repeated readings
- Identify anomalous results by checking whether a value is significantly different from the other repeated readings
- Exclude anomalous results from the calculation of the mean (do not include them when averaging)
Key terms in this question
valid · reliable · anomalous result
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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