Long answer·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 rectangular wire frame carries a soap film. A movable side of length is pulled slowly through . The surface tension of the soap solution is .
Total: 4 marks
(a) Find the increase in area of one surface. (1 mark)
(b) Find the total increase in surface area of the film. (1 mark)
(c) Find the work done. (2 marks)
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