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Question #42552

Difficulty: 8/10 | 🟢 Free

The Question

A cylinder contains nn moles of an ideal monatomic gas. A piston of mass mm and cross-sectional area AA is attached to a spring of constant kk and a damper. The damper exerts a non-linear drag force Fd=−αv3F_d = -\alpha v^3 on the piston, where vv is its velocity and α\alpha is a positive constant. The gas undergoes a forced thermodynamic cycle such that the piston's state traces an ellipse in phase space given by x2x02+p2p02=1\frac{x^2}{x_0^2} + \frac{p^2}{p_0^2} = 1, where xx is the displacement from equilibrium and pp is the momentum. At the state of maximum momentum, the piston's kinetic energy equals the internal energy that nn moles of this gas would have at a reference temperature T0T_0. Assuming the external pressure is zero, what is the net heat ΔQ\Delta Q absorbed by the gas per cycle?

Options

  • A.

    93παx04m3/2(nRT0)3/2\frac{9\sqrt{3}\pi \alpha x_0}{4 m^{3/2}} (n R T_0)^{3/2}

  • B.

    33παx04m3/2(nRT0)3/2\frac{3\sqrt{3}\pi \alpha x_0}{4 m^{3/2}} (n R T_0)^{3/2}

  • C.

    9παx04m3/2(nRT0)3/2\frac{9\pi \alpha x_0}{4 m^{3/2}} (n R T_0)^{3/2}

  • D.

    00

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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

Cyclic Process Geometry|Phase Space Trajectory|Equipartition Theorem

Why This Question Is Tricky

Common Mistakes

The question tests the student's ability to apply the First Law of Thermodynamics to a non-ideal, dissipative mechanical coupling.

A common trap is assuming that the cyclic integral of work ∮PdV\oint P dV is simply the area of the phase space trajectory or zero for a conservative-looking spring system.

Students often fail to recognize that the gas must perform net positive work to continuously overcome the non-linear viscous damping (−αv3-\alpha v^3), meaning the P−VP-V area equals the irreversible energy dissipated per cycle.

Furthermore, it integrates the Equipartition Theorem to establish the momentum amplitude, punishing students who cannot link microscopic thermodynamic states to macroscopic phase space parameters.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterThermodynamics - Class 11 Part 2
ConceptCyclic Process Geometry
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree