Case study·Hard exam skill (4/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
A student stands on a platform at rest on a smooth horizontal floor. The student walks east relative to the platform. There is no external horizontal force on the student-platform system.
Total: 5 marks
(a) Find the total mass of the system. (1 mark)
(b) Explain why the horizontal position of the centre of mass remains fixed. (1 mark)
(c) If the platform shifts metres west, write the centre-of-mass equation. (1 mark)
(d) Find the displacement of the platform. (1 mark)
(e) Find the student's displacement relative to the ground. (1 mark)
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