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Hooke’s law and spring calculations

Use force and extension, find spring constants and elastic energy, and interpret force–extension data.

Practise

Force–extension gradient

A straight force–extension line passes through (extension 0.01 m, force 0.8 N) and (0.09 m, 7.2 N). Force is on the vertical axis. The spring obeys Hooke’s law over this range. Calculate its gradient, which is the spring constant. Give your answer to 3 significant figures.

Treat the given values as exact unless an uncertainty is stated.

Use decimals or e notation, e.g. 4.2e-3. Enter the unit separately.

Hint

Gradient = change in force / change in extension.

Worked solution
  1. k = (7.2 − 0.8) / (0.09 − 0.01) N m⁻¹.
  2. Answer: 80.0 N m⁻¹ (3 significant figures).
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Foundation and Higher: this set covers content common to both tiers. Some calculations need several steps.

Force and extension

Extension is the change from unloaded length, measured in metres for F = kx. The force–extension gradient is k when force is vertical and extension horizontal. E = ½kx² applies over the Hooke’s-law range. The limit of proportionality and elastic limit are different: a curved relationship does not by itself prove permanent deformation.

Work through the practical method and sample results

GCSE scope

AQA 8463: 4.5.3; required practical 6 (selected); OCR Gateway J249: P2.3b–e; PM2.3i–iii; PAG P2 (selected). Tasks cover the selected skills listed above.

AQA specification · OCR Gateway specification