What is the critical design consideration for a keyway in a shaft?

The correct answer is B: Minimize stress concentration factor at the keyway. Keyways create stress concentration points that can lead to fatigue failure; proper design minimizes the stress concentration factor.

A jet of water impinges on a flat plate perpendicular to its surface. If jet velocity is 10 m/s and jet area is 0.01 m², the force on the plate is approximately:

The correct answer is C: 1000 N. Force F = ρAv² = 1000 × 0.01 × 10² = 1000 N (using ρ = 1000 kg/m³ for water)

Which dimensionless number is used to characterize the relative importance of gravity and inertial forces in open channel flow?

The correct answer is B: Froude number. The Froude number Fr = V/√(gD_h) characterizes gravity effects. In open channel flow, it determines flow regime (subcritical Fr1).

For an ideal gas undergoing an isothermal process, the change in internal energy is:

The correct answer is B: Zero. In an isothermal process, temperature is constant. For an ideal gas, internal energy depends only on temperature, so ΔU = 0.

For steady flow of an incompressible fluid through a variable area duct, which equation relates velocities at different sections?

The correct answer is B: Continuity equation (A₁v₁ = A₂v₂). Continuity equation for incompressible flow states Q = constant, so A₁v₁ = A₂v₂

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Mechanical Engineering

Thermodynamics, hydraulics, machine design

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Difficulty: All Easy Medium Hard 51–60 of 82

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.51 Easy Thermodynamics

Which law states that the total energy of an isolated system remains constant?

A Second Law of Thermodynamics

B First Law of Thermodynamics

C Third Law of Thermodynamics

D Zeroth Law of Thermodynamics

Correct Answer: B. First Law of Thermodynamics

EXPLANATION

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

Test

Q.52 Easy Thermodynamics

In a constant volume process (isochoric), if temperature increases from 300 K to 600 K, the pressure ratio P₂/P₁ will be:

A 0.5

B 1.0

C 2.0

D 4.0

Correct Answer: C. 2.0

EXPLANATION

For isochoric process: P/T = constant, so P₂/P₁ = T₂/T₁ = 600/300 = 2.0

Test

Q.53 Easy Thermodynamics

In a Diesel cycle, which process represents constant pressure heat addition?

A Isentropic process

B Isobaric process

C Isochoric process

D Isothermal process

Correct Answer: B. Isobaric process

EXPLANATION

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

Test

Q.54 Easy Thermodynamics

A heat engine operates between two thermal reservoirs at temperatures 600 K and 300 K. What is the maximum possible efficiency of this engine?

A 25%

B 50%

C 75%

D 100%

Correct Answer: B. 50%

EXPLANATION

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

Test

Q.55 Easy Thermodynamics

Which of the following statements about entropy is INCORRECT?

A Entropy is a measure of molecular disorder or randomness

B Entropy always increases for an irreversible adiabatic process

C Entropy of a reversible isothermal process equals Q/T

D Entropy of the universe decreases for spontaneous processes

Correct Answer: D. Entropy of the universe decreases for spontaneous processes

EXPLANATION

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

Test

Q.56 Easy Thermodynamics

The relationship between specific heats Cp - Cv for an ideal gas is:

A Cp - Cv = R

B Cp - Cv = 2R

C Cp = Cv (they are equal)

D Cp - Cv = R/M where M is molar mass

Correct Answer: A. Cp - Cv = R

EXPLANATION

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

Test

Q.57 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.58 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.59 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.60 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

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