Case study·Standard multi-step (3/5)·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 stress-strain test is performed on a metal wire. The graph remains straight up to point P, then bends before the sample finally breaks at B.
Total: 4 marks
(a) Which part of the graph is used to find Young's modulus? (1 mark)
(b) What does departure from the straight line indicate? (1 mark)
(c) Why is the breaking point not used to calculate Young's modulus? (1 mark)
(d) State one design reason engineers keep working stress far below the breaking stress. (1 mark)
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