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Question #42573
The Question
A small solid sphere of mass and density falls through a long column of an incompressible viscous liquid of density (). The liquid is maintained at a constant absolute temperature by a large surrounding thermal reservoir. After the sphere attains a constant terminal velocity, it falls through a further vertical distance . Which of the following expressions represents the total increase in the entropy of the universe (sphere + liquid + reservoir) during the fall through distance ? (Assume acceleration due to gravity is and macroscopic position does not affect the internal entropy of the sphere).
Options
- A.
- B.
- C.
- D.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Intuition_Breaker
Train your brain to resist "obvious" answers that are designed to deceive your intuition.
Concepts Behind This Question
Entropy and Reversibility|State Function vs Path Function|Viscosity and Stokes' Law
Why This Question Is Tricky
Common Mistakes
This question tests the misconception that a process occurring at a constant velocity (terminal velocity) is quasi-static and reversible, leading students to incorrectly conclude that the entropy change of the universe is zero.
In reality, viscous drag is a non-conservative, path-dependent force.
The constant velocity merely indicates a steady state where the net loss of mechanical energy (gravitational potential energy minus buoyant work) is continuously dissipated as heat into the surrounding fluid.
Students must recognize that this irreversible dissipation increases the entropy of the thermal reservoir, bridging classical mechanics and the Second Law of Thermodynamics.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Thermodynamics - Class 11 Part 2 |
| Concept | Entropy and Reversibility |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |