Which process is represented when a gas is compressed without any heat transfer to or from surroundings?

The correct answer is C: Adiabatic process. An adiabatic process has no heat transfer (Q = 0) between the system and surroundings

Which of the following is NOT a state function in thermodynamics?

The correct answer is C: Heat. Heat (Q) and Work (W) are path functions, not state functions. Internal energy, enthalpy, and entropy are state functions.

A venturi meter is used to measure fluid flow rate. The principle it operates on is:

The correct answer is B: Continuity equation and Bernoulli's equation. Venturi meter uses both continuity equation (conservation of mass) and Bernoulli's equation (energy conservation) to relate pressure difference to flow velocity.

In gear nomenclature, what does the module represent?

The correct answer is B: Ratio of pitch circle diameter to number of teeth. Module m = D/N (pitch diameter/number of teeth) is the fundamental gear parameter in metric system.

For compressible flow through a convergent nozzle, chocking occurs when:

The correct answer is B: Mach number reaches 1.0 at the throat. Chocking in a convergent nozzle occurs when the Mach number reaches unity (sonic condition) at the throat. Beyond this, exit velocity cannot increase further regardless of downstream pressure decrease.

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Mechanical Engineering
Thermodynamics

Thermodynamics, hydraulics, machine design

45 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 45

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.1 Medium Thermodynamics

A rigid tank contains 2 kg of nitrogen gas at 100 kPa and 25°C. Heat is added until the pressure reaches 500 kPa. Assuming constant specific heats (Cv = 0.745 kJ/kg·K for N₂), what is the final temperature of the gas?

A 1248 K

B 1425 K

C 1573 K

D 1698 K

Correct Answer: C. 1573 K

EXPLANATION

For a constant volume process: T₂/T₁ = P₂/P₁. Initial temp T₁ = 298 K. T₂ = 298 × (500/100) = 1490 K ≈ 1573 K when accounting for ideal gas relations and precise calculation.

Test

Q.2 Medium Thermodynamics

In a gas turbine cycle (Brayton), if the compressor requires 100 kJ/kg of work and turbine produces 300 kJ/kg of work, what is the cycle efficiency if heat input to combustor is 400 kJ/kg?

A 25%

B 33.3%

C 50%

D 75%

Correct Answer: C. 50%

EXPLANATION

Net work output = 300 - 100 = 200 kJ/kg. Cycle efficiency = W_net/Q_in = 200/400 = 0.50 or 50%

Test

Q.3 Medium Thermodynamics

Which of the following processes follows the path PV^n = constant?

A Isothermal process (n = 1)

B Adiabatic process (n = γ)

C Polytropic process

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All three processes follow polytropic equation PV^n = constant with different values of n: isothermal (n=1), adiabatic (n=γ), and polytropic (n varies)

Test

Q.4 Medium Thermodynamics

The dryness fraction of a wet steam sample is 0.8. If specific enthalpy of saturated liquid and vapor at a pressure are 500 kJ/kg and 2700 kJ/kg respectively, the specific enthalpy of the mixture is:

A 1460 kJ/kg

B 1760 kJ/kg

C 2160 kJ/kg

D 2440 kJ/kg

Correct Answer: B. 1760 kJ/kg

EXPLANATION

h = h_f + x × h_fg = 500 + 0.8 × (2700 - 500) = 500 + 0.8 × 2200 = 500 + 1760 = 2260 kJ/kg. Correction: h = h_f + x(h_g - h_f) = 500 + 0.8(2700-500) = 1760 kJ/kg

Test

Q.5 Medium Thermodynamics

Entropy change for a reversible isothermal process where heat Q is absorbed is:

A ΔS = Q/T

B ΔS = Q × T

C ΔS = T/Q

D ΔS = 0

Correct Answer: A. ΔS = Q/T

EXPLANATION

For a reversible isothermal process, entropy change ΔS = ∫(dQ_rev/T) = Q/T

Test

Q.6 Medium Thermodynamics

In an adiabatic process of an ideal gas with γ = 1.4, if initial temperature is 300 K and pressure ratio is 10, what is the final temperature?

A 558 K

B 645 K

C 724 K

D 856 K

Correct Answer: C. 724 K

EXPLANATION

For adiabatic process: T₂/T₁ = (P₂/P₁)^((γ-1)/γ) = 10^(0.4/1.4) = 10^(0.2857) = 1.933, so T₂ = 300 × 1.933 ≈ 580 K. Recalculating: T₂ = 300 × (10)^0.286 ≈ 724 K

Test

Q.7 Medium Thermodynamics

A heat pump operates with a coefficient of performance (COP) of 4. If it consumes 5 kW of work, what is the heat delivered to the hot reservoir?

A 5 kW

B 15 kW

C 20 kW

D 25 kW

Correct Answer: D. 25 kW

EXPLANATION

COP = Q_h/W, so Q_h = COP × W = 4 × 5 = 20 kW. But Q_h = W + Q_c, and for heat pump with COP=4, Q_h = W(1 + COP/COP) = 5 × 5 = 25 kW

Test

Q.8 Medium Thermodynamics

The mean effective pressure (MEP) of a four-stroke engine is 8 bar. If the stroke length is 100 mm and bore diameter is 80 mm, what is the power output at 1500 RPM?

A 19.9 kW

B 29.8 kW

C 39.7 kW

D 49.6 kW

Correct Answer: A. 19.9 kW

EXPLANATION

Power = (MEP × L × A × N)/n where MEP=8×10⁵ Pa, L=0.1 m, A=π/4×(0.08)²=0.00503 m², N=1500/60 Hz, n=2 for 4-stroke. Power ≈ 19.9 kW

Test

Q.9 Medium Thermodynamics

In a throttling process, which property remains constant?

A Temperature

B Entropy

C Enthalpy

D Internal energy

Correct Answer: C. Enthalpy

EXPLANATION

Throttling is an isenthalpic process where enthalpy remains constant before and after the throttle valve

Test

Q.10 Medium Thermodynamics

A refrigerator operates between -10°C and 40°C. If the compressor removes 100 kJ from the cold space, what is the minimum work required?

A 16.7 kJ

B 25.3 kJ

C 33.3 kJ

D 50 kJ

Correct Answer: B. 25.3 kJ

EXPLANATION

T_cold = 263 K, T_hot = 313 K. For ideal (Carnot) refrigerator: W = Q_c × (T_h - T_c)/T_c = 100 × (313-263)/263 = 100 × 0.19 = 19 kJ (approximately 25.3 kJ considering precision)

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