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 student studies a small oil drop moving through glycerine. The drop first accelerates, then moves downward with constant speed. The teacher says this final constant speed can be used to estimate viscosity.
Total: 4 marks
(a) Name the final constant speed. (1 mark)
(b) List the three forces acting on the drop while it falls. (1 mark)
(c) At the final constant speed, what is the net force on the drop? (1 mark)
(d) Why is a larger drop expected to have a larger final speed in the same liquid? (1 mark)
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