H1 Physics 8867 · Nov 2023PhysicsPaper 1Most challenging

Paper 1 Q7 — Impulse, step by step

Dynamics — impulse as area under F–t graph and change in momentum (vector!)

What the examiners said

“Most candidates found this question difficult. The key… was the least popular option and chosen only by candidates who performed well overall. There were several steps involved which made the question challenging.” The general comments also flagged impulse questions as challenging.

Try the question (reconstruction)

A ball of mass 0.20 kg travelling at 5.0 m s⁻¹ strikes a wall at right angles and rebounds along the same line. The force on the ball varies with time as a triangle of peak force 40 N lasting 0.060 s. What is the rebound speed of the ball?

Examiner report: “Several steps were involved; only strong candidates chose the key.”

Explore — impulse = area = change in momentum

Adjust the peak force and contact time. The shaded area is the impulse; the momentum bars show why the initial momentum must be counted with a negative sign.

Peak force F_max (N): 40 Contact time (s): 0.060

Try reducing F_max until the rebound speed hits zero — the impulse then exactly cancels the incoming momentum (J = mu = 1.0 N s).

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