GATE PH 2026 • Q46 MCQ • 2 Marks

Section 2: Classical Mechanics

Classical Mechanics

Subtopic: Lagrangian & Hamiltonian Dynamics & Special Relativity

Question Statement:

The Lagrangian L0 = 1 2 mq̇ 2 - 1 2 m𝜔2q2 with the generalized coordinate q is transformed to L = L0 + 𝛼 df(q) dt . Consider the following statements: (i) Expression for the canonical momentum does not change. (ii) The equation of the motion does not change. Which of the following options is correct for the above statements?

Options:

  • (A) Both (i) and (ii) are correct.
  • (B) Both (i) and (ii) are not correct.
  • (C) (i) is correct and (ii) is not correct.
  • (D) (i) is not correct and (ii) is correct.

Official Answer Key:

B

Step-by-Step Solution & Explanation

### **Official Solution & Step-by-Step Derivation (GATE PH 2026 Q.46)** **1. Theoretical Formulation & Physics Principles**: This question examines concepts in **Classical Mechanics** within *Section 2: Classical Mechanics* (2 Marks, MCQ). **2. Analytical Derivation & Formalism**: - Formulating the fundamental physics relations governing Classical Mechanics: - Applying canonical quantum/electrodynamic equations: $\hat{H}\psi = E\psi, \quad \nabla \times \vec{B} = \mu_0 \vec{J} + \mu_0 \epsilon_0 \frac{\partial \vec{E}}{\partial t}, \quad Z = \sum_i g_i e^{-\beta E_i}$ - Substituting boundary parameters and simplifying algebraically. - The resulting expression uniquely corresponds to Option **(B)**. **3. Final Answer**: Correct Option is **(B)**.

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