H1 Physics 8867 · Nov 2023PhysicsPaper 1Most challenging

Paper 1 Q10 — Moments: sin, cos, and moment arms

Forces — taking moments about a point; perpendicular distances

What the examiners said

“All three distractors were chosen fairly evenly… Candidates mixed up sine and cosine when taking moments or got the distances from the wall wrong.”

Try the question (reconstruction)

A uniform ladder of weight 200 N and length 4.0 m rests with its base on rough ground and its top against a smooth wall, at 60° to the horizontal. What is the normal force from the wall on the ladder?

Examiner report: “Candidates mixed up sine and cosine when taking moments or got the distances from the wall wrong.”

Explore — see the moment arms

Drag the angle. The dashed lines are the true perpendicular distances from the pivot (base). Toggle the misconception to see what swapping sin and cos predicts.

Angle θ (°): 60 show sin↔cos misconception

Physical check: steepen the ladder towards vertical — the wall barely needs to push (N → 0). The swapped formula predicts the opposite, so it must be wrong.

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.

Made by lookang, using Claude Fable 5. More resources: iwant2study.org