Mechanical Engineering - MCQ Practice Questions

For isothermal process: ΔS = Q/T = $\frac{5000}{300}$ = 16.67 J/K. Change in entropy is positive as heat is absorbed.

Heat (Q) and Work (W) are path functions, not state functions. Internal energy, enthalpy, and entropy are state functions.

For monoatomic gases: Cv = ($\frac{3}{2}$)R; for diatomic: Cv = ($\frac{5}{2}$)R; for polyatomic: Cv = ($\frac{7}{2}$)R

Carnot efficiency = 1 - (T_cold/T_hot) = 1 - ($\frac{300}{600}$) = 0.5 = 50%

These are the critical constants for water. This falls within standard thermodynamic property tables for water.

Latent heat is absorbed during vaporization and released during condensation. Both statements are correct.

Mayer's relation: Cp - Cv = R (per mole). This is fundamental for ideal gases.

The Second Law states entropy of the universe INCREASES (ΔS_universe > 0) for spontaneous/irreversible processes, not decreases.

Maximum efficiency of a heat engine = 1 - (T_cold/T_hot) = 1 - ($\frac{300}{600}$) = 0.50 or 50% (Carnot efficiency)

The Diesel cycle has constant pressure heat addition (isobaric process) between the initial compression and subsequent expansion, distinguishing it from the Otto cycle

For isochoric process: P/T = constant, so P₂/P₁ = T₂/T₁ = $\frac{600}{300}$ = 2.0

The First Law of Thermodynamics is the conservation of energy principle for thermodynamic systems

An adiabatic process has no heat transfer (Q = 0) between the system and surroundings

Using ideal gas law PV = nRT: T₂/T₁ = (P₂V₂)/(P₁V₁) = (2P₁ × 2V₁)/(P₁V₁) = 4

From First Law: ΔU = Q - W = 50 - 30 = 20 kJ (taking work done by system as positive)

Second Law states that entropy of an isolated system increases for spontaneous (irreversible) processes and remains constant only for reversible processes