Paper 1 Q3 — Impulse is not work

Dynamics — impulse (=Ft, =Δp) versus work done (=Fs, =ΔKE)

What the examiners said

“The most common incorrect answer was option B, which implies candidates confused impulse with work done.”

Try the question (reconstruction)

A constant force of 6.0 N acts on a 2.0 kg trolley (initially at rest) for 4.0 s, over which it moves 24 m. What is the impulse delivered to the trolley?

Examiner report: “The common wrong answer used F×s (work, in joules) instead of F×t (impulse, in N s).”

Explore — time builds momentum, distance builds energy

A constant force pushes the trolley. Watch impulse (F×t) and work (F×s) grow at different rates — they are different quantities with different units.

Force F (N): 6 Time elapsed (s): 4.0

Momentum answers ‘how hard, for how long’ (N s); energy answers ‘how hard, over what distance’ (J). Never interchange them.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H2 Physics 9749 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

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