The Strouhal number is used to characterize:

The correct answer is B: Vortex shedding and oscillating flow phenomena. Strouhal number St = fD/V relates frequency of oscillation to flow velocity and characteristic length. It's crucial in analyzing vortex shedding from cylinders.

What is the dimension of pressure coefficient (Cₚ)?

The correct answer is A: Dimensionless. Pressure coefficient Cₚ = (P - P∞)/(0.5ρV∞²) is a dimensionless quantity used in aerodynamics and fluid mechanics.

In a gas turbine Brayton cycle, air enters the compressor at 300 K and 100 kPa. The pressure ratio is 8. If γ = 1.4 and R = 287 J/kg·K, find the compressor outlet temperature (assuming isentropic compression).

The correct answer is B: 520.2 K. T_2/T_1 = (P_2/P_1)^((γ-1)/γ) = 8^(0.4/1.4) = 8^0.2857 ≈ 1.734. T_2 = 300 × 1.734 ≈ 520.2 K

A cast iron machine bed is subjected to fluctuating loads. Which material property is MOST important for its long-term reliability?

The correct answer is B: Fatigue strength and damping capacity. Cast iron's excellent damping capacity and reasonable fatigue strength make it ideal for machine beds subjected to fluctuating loads. Its ability to absorb vibration is a key advantage for structural components.

In power screw design, what does the 'efficiency' of a screw represent?

The correct answer is A: Ratio of output power to input power. Screw efficiency = (Load × pitch)/(2π × effort × radius). It represents the ratio of useful work output to the energy input, typically ranging from 25-90%.

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Mechanical Engineering
Thermodynamics

Thermodynamics, hydraulics, machine design

36 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 36

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.11 Easy Thermodynamics

The enthalpy of vaporization (latent heat) of water at 100°C is 2257 kJ/kg. This represents:

A The heat needed to convert 1 kg of liquid water to steam at constant temperature and pressure

B The heat released when steam condenses

C Both (a) and (b)

D The sensible heat of water

Correct Answer: C. Both (a) and (b)

EXPLANATION

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

Test

Q.12 Easy Thermodynamics

A substance has a critical temperature Tc=647 K and critical pressure Pc=22.1 MPa. This is most likely:

A Nitrogen

B Water

C Carbon dioxide

D Oxygen

Correct Answer: B. Water

EXPLANATION

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

Test

Q.13 Easy Thermodynamics

A carnot engine operates between 600 K and 300 K. The maximum possible efficiency is:

A 25%

B 50%

C 75%

D 100%

Correct Answer: B. 50%

EXPLANATION

Carnot efficiency = 1 - (T_cold/T_hot) = 1 - (300/600) = 0.5 = 50%

Test

Q.14 Easy Thermodynamics

The specific heat capacity at constant volume (Cv) for a monoatomic ideal gas is:

A (3/2)R per mole

B (5/2)R per mole

C (7/2)R per mole

D R per mole

Correct Answer: A. (3/2)R per mole

EXPLANATION

For monoatomic gases: Cv = (3/2)R; for diatomic: Cv = (5/2)R; for polyatomic: Cv = (7/2)R

Test

Q.15 Easy Thermodynamics

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

A Internal Energy

B Enthalpy

C Heat

D Entropy

Correct Answer: C. Heat

EXPLANATION

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

Test

Q.16 Easy Thermodynamics

A reversible isothermal process occurs at 300 K for an ideal gas. If 5 kJ of heat is absorbed, what is the change in entropy of the system?

A 16.67 J/K

B 0.0167 J/K

C 1500 J/K

D 0 J/K

Correct Answer: A. 16.67 J/K

EXPLANATION

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

Test

Q.17 Easy Thermodynamics

A gas mixture contains N2 (40%) and O2 (60%) by mole fraction. What is the partial pressure of N2 if total pressure is 5 bar?

A 2 bar

B 3 bar

C 2.5 bar

D 1.5 bar

Correct Answer: A. 2 bar

EXPLANATION

By Dalton's law: P_N2 = x_N2 × P_total = 0.40 × 5 = 2 bar

Test

Q.18 Easy Thermodynamics

For a substance, the triple point and critical point data are important in phase diagrams. At the triple point, how many phases can coexist?

A One phase only

B Two phases can coexist

C All three phases (solid, liquid, vapor) coexist

D Only solid and vapor phases exist

Correct Answer: C. All three phases (solid, liquid, vapor) coexist

EXPLANATION

At the triple point, solid, liquid, and vapor phases are in thermodynamic equilibrium. For water, this occurs at 273.16 K and 611.657 Pa.

Test

Q.19 Easy Thermodynamics

Which statement correctly describes the second law of thermodynamics?

A Total energy of universe remains constant

B Entropy of an isolated system never decreases; it increases for irreversible processes

C Heat always flows from cold to hot body

D All heat absorbed by a system is converted to work

Correct Answer: B. Entropy of an isolated system never decreases; it increases for irreversible processes

EXPLANATION

The Clausius statement of second law: For isolated systems, dS_universe ≥ 0. dS = 0 for reversible, dS > 0 for irreversible processes.

Test

Q.20 Easy Thermodynamics

Which of the following processes has zero work done by/on the gas?

A Isobaric process

B Isochoric (constant volume) process

C Isothermal process

D Adiabatic process

Correct Answer: B. Isochoric (constant volume) process

EXPLANATION

Work W = ∫P dV. In isochoric process, dV = 0, therefore W = 0 regardless of pressure or temperature changes.

Test

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