BE/B Eng Bachelor of Engineering Mechanical Engineering 1 — Questions and Answers
Question 1: Which law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another?
- First Law (Correct answer)
- Second Law
- Third Law
- Zeroth Law
Correct answer: First Law
The First Law of Thermodynamics is the law of energy conservation: the total energy of an isolated system remains constant.
Question 2: What does the second law of thermodynamics imply about the entropy of an isolated system?
- Entropy always increases or remains constant (Correct answer)
- Entropy always decreases
- Entropy remains exactly constant
- Entropy is undefined for isolated systems
Correct answer: Entropy always increases or remains constant
The Second Law states that the entropy of an isolated system tends to increase over time, indicating the direction of spontaneous processes.
Question 3: In stress-strain analysis, Young's Modulus is defined as the ratio of:
- Stress to strain in the elastic region (Correct answer)
- Strain to stress in the plastic region
- Shear stress to shear strain
- Ultimate stress to yield stress
Correct answer: Stress to strain in the elastic region
Young's Modulus (E) = σ/ε, where σ is axial stress and ε is axial strain, applicable within the linear elastic region of a material.
Question 4: What is the efficiency of an ideal Carnot heat engine operating between temperatures T_H = 600 K and T_C = 300 K?
- 50% (Correct answer)
- 25%
- 75%
- 100%
Correct answer: 50%
Carnot efficiency η = 1 - T_C/T_H = 1 - 300/600 = 0.50, or 50%; no real engine can exceed this limit between these temperatures.
Question 5: Which type of stress acts perpendicular to the cross-sectional area of a member?
- Normal stress (Correct answer)
- Shear stress
- Torsional stress
- Bearing stress
Correct answer: Normal stress
Normal stress (σ = F/A) acts perpendicular (normal) to the cross-section, either as tension (pulling) or compression (pushing).
Question 6: In fluid mechanics, what does the Reynolds number represent?
- The ratio of inertial forces to viscous forces in a fluid flow (Correct answer)
- The ratio of pressure forces to surface tension
- The ratio of buoyancy to viscous forces
- The ratio of thermal to momentum diffusivity
Correct answer: The ratio of inertial forces to viscous forces in a fluid flow
The Reynolds number (Re = ρVL/μ) indicates whether a flow is laminar (low Re) or turbulent (high Re) by comparing inertial and viscous forces.
BE/B Eng Bachelor of Engineering Mechanical Engineering 1
Which law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another?