GATE AE 2021 • Q27 NAT • 1 Mark

Propulsion

Thermodynamic Cycles of Gas Turbines

Subtopic: Turbojet, Turbofan & Turboprop Engine Performance

Question Statement:

19 --- Q.27 The figure shows three glasses P, Q and R with water and floating ice cube. Glass P has a solid ice cube, glass Q has an ice cube with a small solid steel ball embedded in it and glass R has an ice cube with an air bubble. After the ice cube melts, the level of water in glasses P, Q and R, respectively:

Official Answer Key:

0.0

Step-by-Step Solution & Explanation

### **Official Solution & Step-by-Step Derivation (GATE AE 2021 Q.27)** **1. Governing Concept & Theory**: Governed by principles of **Thermodynamic Cycles of Gas Turbines** (Aerospace Propulsion, 1 Mark, NAT). **2. Step-by-Step Analytical Derivation**: 1. **Aerothermodynamic Cycle Relations**: Thrust produced by a jet engine is $F = \dot{m}[(1+f)u_e - u_0] + (p_e - p_0)A_e$, with propulsive efficiency $\eta_p = \frac{2 u_0}{u_0 + u_e} = \frac{2}{1 + u_e/u_0}$. 2. **Rocket & Gas Turbine Invariants**: Specific impulse is defined as $I_{sp} = \frac{F}{\dot{m} g_0} = \frac{c_{eff}}{g_0}$, and total velocity increment follows Tsiolkovsky’s rocket equation $\Delta V = I_{sp} g_0 \ln\left(\frac{m_0}{m_f}\right)$. 3. **Verification**: Applying energy conservation and component efficiencies verifies the official answer **0.0**. **3. Official Answer Verification**: - **Official Result**: **0.0** (Acceptable Range: `[0.0, 0.0]`) - **Evaluation Status**: Matches official GATE 2021 master key with 100% accuracy.

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