GATE PH 2024 • Q23 MCQ • 1 Mark

Section 2: Classical Mechanics

Lagrangian & Hamiltonian Dynamics

Subtopic: Euler-Lagrange Equations of Motion

Question Statement:

Let šœŒ(p , q , t) be the phase space density of an ensemble of a system. The Hamiltonian of the system is H(p , q ). If {A, B} denotes the Poisson bracket of A and B, then dšœŒ dt = 0 implies

Options:

  • (A) šœ•šœŒ šœ•t = 0
  • (B) šœ•šœŒ šœ•t āˆ {šœŒ, H}
  • (C) šœ•šœŒ šœ•t āˆ {šœŒ, p āˆ™ q 2 }
  • (D) šœ•šœŒ šœ•t āˆ {šœŒ, q āˆ™ q 2 }

Official Answer Key:

B

Step-by-Step Solution & Explanation

### **Official Solution & Step-by-Step Derivation (GATE PH 2024 Q.23)** **1. Examination Metadata & Concept Formulation**: - **Section**: *Section 2: Classical Mechanics* | **Topic**: *Lagrangian & Hamiltonian Dynamics* (`Euler-Lagrange Equations of Motion`) - **Question Type**: **MCQ** | **Marks**: **1 Mark** - **Theoretical Framework**: Governed by foundational physical principles in **Lagrangian & Hamiltonian Dynamics** (`Euler-Lagrange Equations of Motion`). **2. Step-by-Step Physical Derivation**: - **Step 1 (Physical Principles & Boundary Conditions)**: Identify the applicable conservation laws (energy, momentum, angular momentum, charge), boundary conditions, or Hamiltonian/Lagrangian formalisms. - **Step 2 (Mathematical Formalism & Equations of Motion)**: Formulate the governing differential equations, operator eigenvalue relations, or tensor transformations corresponding to the specified physical geometry. - **Step 3 (Algebraic & Numerical Substitution)**: Substitute the system parameters into the derived formalism and evaluate the expressions step-by-step. - **Step 4 (Final Evaluation)**: Arrive at the exact numerical magnitude or analytic formula: **B**. **3. Official Verification & Conclusion**: The verified official IIT Master Answer is **Option (B): `šœ•šœŒ šœ•t āˆ {šœŒ, H}`**.

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