H1 Physics 8867 · Nov 2023PhysicsPaper 2Widespread errors

Paper 2 Q2 — Spring energy: areas, squares and the forgotten g.p.e.

Work & energy — EPE from an F–x graph; (a−b)² ≠ a²−b²; energy bookkeeping on release

What the examiners said

“A large proportion of candidates… did not appreciate that (a − b)² is not the same as a² − b². Other common errors were incorrect or missing conversion of cm to m… many omitted consideration of gravitational potential energy… Some attempted kinematics equations, not realising the acceleration is non-uniform.”

Item 1 — energy change between two extensions

A spring (k = 27 N m⁻¹) obeys Hooke’s law. Its extension is increased from 3.5 cm to 6.5 cm. What is the increase in elastic potential energy?

Examiner report: “Candidates did not appreciate that (a − b)² is not the same as a² − b²; cm→m conversions were missed.”

Item 2 — what happens on release

A mass hangs at rest on the stretched spring, pulled below its equilibrium position and released. Which energy statement about the instant it passes back through a higher point is correct?

Examiner report: “Many omitted gravitational potential energy; some used kinematics though acceleration is non-uniform.”

Explore — energy stores of a mass on a spring

Pull the mass below equilibrium with the slider, then press release. The bars track the three energy stores. Toggle the misconception to see the error from ignoring g.p.e.

Initial pull below equilibrium (cm): 3.0 misconception: ignore g.p.e.

With the misconception box ticked, the bars stop adding up — the ‘missing’ energy is exactly the gravitational PE the examiners said candidates omitted.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Physics 8867 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

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