Long answer·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 small metal sphere of radius falls through a liquid. The density difference between the sphere and liquid is and the liquid viscosity is . Take .
Total: 4 marks
(a) Write the expression for terminal velocity according to Stokes' law. (1 mark)
(b) Find the terminal velocity. (2 marks)
(c) State why the speed becomes constant at terminal velocity. (1 mark)
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