Mechanical Engineering Mock Interview Questions & Practice

State the Second Law of Thermodynamics and explain its significance.

Key points to cover:

• Heat cannot spontaneously flow from a colder to a hotter body
• Or: entropy of an isolated system never decreases
• Establishes the direction of natural processes

What is the Otto cycle, and what type of engine does it model?

Key points to cover:

• Two isentropic and two constant-volume processes
• Models a spark-ignition (petrol) internal combustion engine
• Notes the idealized nature of the cycle

What is thermal conductivity, and what does it indicate about a material?

Key points to cover:

• A material property indicating how well it conducts heat
• Heat flux per unit temperature gradient
• Higher value means the material transfers heat more readily

What is hydrostatic pressure, and how does it vary with depth in a fluid?

Key points to cover:

• Pressure exerted by a fluid at rest due to the weight of fluid above
• Increases linearly with depth
• Proportional to fluid density, gravitational acceleration, and depth

What is the Reynolds number, and what does it indicate about a flow?

Key points to cover:

• A dimensionless ratio of inertial forces to viscous forces
• Used to predict whether a flow will be laminar or turbulent
• With a critical value marking the transition

What is cavitation in a centrifugal pump, and what conditions promote it?

Key points to cover:

• Local pressure inside the pump drops below the fluid's vapor pressure
• Vapor bubbles form and then collapse violently
• Promoted by insufficient suction head or excessive pump speed

What is Hooke's Law, and within what range of deformation does it apply?

Key points to cover:

• Stress is directly proportional to strain
• Proportionality constant is the material's modulus of elasticity
• Applies only within the elastic limit

What is a bending moment diagram, and what information does it provide?

Key points to cover:

• A graphical representation of bending moment along a beam
• Provides the location and magnitude of maximum bending stress
• Essential for beam design

What is stress concentration, and what commonly causes it in a machine component?

Key points to cover:

• A localized increase in stress at a geometric discontinuity
• Well above the average stress in the surrounding material
• Commonly caused by abrupt changes in cross-section or geometry

What is the difference between hot working and cold working in metal forming processes?

Key points to cover:

• Hot working: above the material's recrystallization temperature
• Allows significant deformation without work hardening
• Cold working: below recrystallization, results in work hardening

What is cutting speed in machining, and how does it affect tool life and surface finish?

Key points to cover:

• The relative velocity between cutting tool and workpiece surface
• Higher speeds increase material removal rate
• Can reduce tool life due to increased heat generation

What is the difference between MIG (GMAW) and TIG (GTAW) welding?

Key points to cover:

• MIG uses a continuously fed consumable wire electrode
• Plus a shielding gas
• TIG uses a non-consumable tungsten electrode with a separate filler rod

What is Grubler's equation, and what is it used to determine?

Key points to cover:

• Relates the number of links, joints, and degrees of freedom
• In a planar mechanism
• Used to determine a mechanism's mobility

What is the difference between spur gears and helical gears?

Key points to cover:

• Spur gears: teeth parallel to the axis, simpler but noisier
• Helical gears: teeth cut at an angle, smoother/quieter
• Helical gears introduce an axial thrust load

What is resonance in the context of mechanical vibrations, and why can it be dangerous?

Key points to cover:

• The forcing frequency matches (or is close to) a system's natural frequency
• Causes the amplitude of vibration to increase dramatically
• Can cause structural damage or failure