Mechanical Engineering core subjects
Mechanical Engineering core tests thermodynamics, fluid mechanics, strength of materials, theory of machines, manufacturing, machine design, and heat transfer. The exam favours formula application with correct units and sign conventions.
Core rules and concepts
- Thermodynamics: for a reversible heat engine, η = 1 − T_L/T_H, with temperatures in kelvin. COP of a refrigerator = Q_L/W; of a heat pump = Q_H/W.
- Fluid mechanics: continuity A₁V₁ = A₂V₂; Bernoulli p/γ + V²/2g + z = constant along a streamline for ideal flow. Reynolds number Re = ρVD/μ distinguishes laminar and turbulent flow.
- Strength of materials: bending stress σ = My/I; torsion τ = Tr/J; Euler buckling load P_cr = π²EI/L_e².
- Theory of machines: velocity ratio, gear train, and governor sensitivity; Coriolis acceleration appears when a point moves along a rotating body.
- Manufacturing: casting, welding, machining, and tolerances; know the difference between accuracy and precision.
- Heat transfer: Fourier conduction q = −kA dT/dx; Newton cooling q = hA(T_s − T_∞).
Worked example
A Carnot engine operates between 600 K and 300 K. Efficiency = 1 − 300/600 = 0.50, or 50%. If the same temperatures are given as 327°C and 27°C, convert first: 600 K and 300 K. Using Celsius directly gives a meaningless 1 − 27/327.
Traps
Gauge pressure versus absolute pressure; Celsius versus kelvin; and sign convention for work and heat. In beam problems, a sagging moment is often positive, but follow the convention stated. In fluid flow, Bernoulli is not valid across a pump, turbine, or large friction loss without adding head terms. In manufacturing, do not confuse tolerance with clearance.