5.4 Investigating Hooke's law — Practise
Work independently. The questions and answers are shown together at the end.
These questions are about the investigation itself — the readings, the graph and what it tells you — as well as the arithmetic. Where a question asks you to explain, write a sentence rather than a number.
- In an experiment, a force of 2.0 N gives an extension of 0.05 m and a force of 6.0 N gives 0.15 m. Calculate the spring constant from these two readings.
- H An extension is measured as 0.050 m on a metre stick read to the nearest millimetre. Calculate the percentage uncertainty in the extension.
Answers and concise solutions
1. Spring constant from the gradient
Answer: . The spring constant is the gradient of the force-extension graph, so a graph is a better way to find it than a single pair of readings: a straight line through every point shows that the spring stayed within its limit of proportionality.
2. Percentage uncertainty
Answer: The reading uncertainty is , since the stick is read to the nearest millimetre. So the percentage uncertainty is .