Physics I / Problem-Solving: Waves, Fluids, and Thermodynamics
Practice question · Multiple choice

Waves, fluids and thermodynamics all use conservation laws, but the useful conserved quantity differs. How can you tell which one to reach for?

Hints
  1. Ask what is crossing the boundary of the system in each case.
  2. A conservation law is only useful where nothing leaks.
Show the answer

C. What the system exchanges with its surroundings

Why

A quantity is conserved when nothing carries it across the boundary. Identifying the system and its boundary first is what selects the law, which is why "what is the system?" is the first question in every one of these problems.

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