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Question #42556
The Question
A refrigerator is powered entirely by a decelerating flywheel-generator system. The flywheel has a moment of inertia and an initial angular velocity . The generator experiences a magnetic damping torque due to eddy currents given by , where and is the instantaneous angular velocity. The mechanical power dissipated by this damping is converted entirely into electrical power to drive the refrigerator. The coefficient of performance (COP) of the refrigerator varies with the instantaneous angular velocity and is given by , where . What is the total heat extracted from the cold reservoir as the flywheel comes to a complete stop?
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
Refrigerator Coefficient of Performance|Eddy Currents Dissipation|Conservative Force Field
Why This Question Is Tricky
Common Mistakes
This question tests the integration of a thermodynamic process over a non-steady-state power input driven by electromagnetic damping.
Students commonly fall into the trap of calculating the total initial kinetic energy () and multiplying it by either the initial COP () or a linear average COP ().
By making the COP dependent on the decaying angular velocity, the problem forces a differential setup where cooling power must be integrated over time or angular velocity, revealing that the total heat extracted depends on the weighted integral of the COP, not a simple static average.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Thermodynamics - Class 11 Part 2 |
| Concept | Refrigerator Coefficient of Performance |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |