Which of the following statements about boundary layers is correct?

The correct answer is C: Boundary layer develops due to viscous effects near the surface. Boundary layer develops due to viscous effects that cause velocity gradient near solid surfaces, creating shear stress.

In a constant volume process, 300 J of heat is removed from a gas. Calculate the work done and change in internal energy.

The correct answer is A: W = 0, ΔU = -300 J. In constant volume process: W = ∫PdV = 0. From first law: ΔU = Q - W = -300 - 0 = -300 J

A rotating shaft experiences combined bending and torsional stresses. Which failure theory is MOST appropriate for ductile materials?

The correct answer is B: Maximum shear stress theory (Guest's theory). Maximum shear stress theory (or von Mises equivalent) is most appropriate for ductile materials under combined loading as it accurately predicts failure based on distortion energy.

A gear pair is designed with a contact ratio of 1.4. What does this indicate about the gear mesh?

The correct answer is B: Average of 1.4 teeth are in contact, with mostly one and occasionally two teeth. A contact ratio of 1.4 means that on average 1.4 teeth are in mesh. Typically, one tooth carries the load while occasionally two teeth share the load briefly, ensuring smooth transmission.

A fluid element has shear stress τ = 0.5 Pa and velocity gradient du/dy = 10 s⁻¹. The dynamic viscosity of the fluid is:

The correct answer is A: 0.05 N·s/m². From Newton's law of viscosity, τ = μ(du/dy), so μ = τ/(du/dy) = 0.5/10 = 0.05 N·s/m²

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Mechanical Engineering
Thermodynamics

Thermodynamics, hydraulics, machine design

45 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–45 of 45

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.41 Medium Thermodynamics

The polytropic process for an ideal gas follows PV^n = constant. When n = 0, the process is:

A Isobaric

B Isochoric

C Isothermal

D Adiabatic

Correct Answer: A. Isobaric

EXPLANATION

When n = 0, PV⁰ = P = constant, which is an isobaric process. When n = 1 (isothermal), n = γ (adiabatic), n = ∞ (isochoric).

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Q.42 Medium Thermodynamics

For a real gas, the compressibility factor Z is defined as:

A Z = PV/nRT

B Z = nRT/PV

C Z = P/VT

D Z = V/nRT

Correct Answer: A. Z = PV/nRT

EXPLANATION

Compressibility factor Z = PV/(nRT). For ideal gas, Z = 1. For real gases, Z ≠ 1 due to molecular interactions.

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Q.43 Medium Thermodynamics

The availability or exergy of a system is zero when the system is in:

A Dead state

B Reference state

C Critical state

D Triple point

Correct Answer: A. Dead state

EXPLANATION

Exergy is maximum work available from a system. At dead state (T₀, P₀, same as surroundings), exergy is zero as no useful work can be extracted.

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Q.44 Medium Thermodynamics

In a throttling process (Joule-Thomson expansion), the enthalpy of the fluid:

A Increases

B Decreases

C Remains constant

D Becomes zero

Correct Answer: C. Remains constant

EXPLANATION

Throttling is an isenthalpic process where enthalpy remains constant (H_initial = H_final) as the fluid expands through a restriction.

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Q.45 Medium Thermodynamics

A heat engine operating between two temperature reservoirs has a maximum theoretical efficiency given by:

A Carnot efficiency: η = 1 - (T_C/T_H)

B η = T_C/T_H

C η = T_H - T_C

D η = (T_H - T_C)/T_C

Correct Answer: A. Carnot efficiency: η = 1 - (T_C/T_H)

EXPLANATION

The Carnot efficiency is the maximum theoretical efficiency for any heat engine, given by η = 1 - (T_C/T_H), where temperatures are in Kelvin.

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