Part-A: General Engineering (Mechanical)
Part-A General Engineering (Mechanical)
Part-A of SSC JE Paper-I tests breadth across core mechanical subjects at objective level. Expect 100 questions across engineering mechanics, strength of materials, thermodynamics, fluid mechanics, production engineering, and machine design. The goal is fast recall of definitions, formulas, and standard values.
Core rules and concepts
- Engineering mechanics: resolve forces, draw free-body diagrams, apply equilibrium (ΣF=0, ΣM=0); friction angle = tan⁻¹μ.
- Strength of materials: stress = P/A, strain = ΔL/L, Young's modulus E = stress/strain; bending equation M/I = σ/y = E/R; torsion T/J = τ/r.
- Thermodynamics: first law Q = ΔU + W; for steady flow, h₁ + V₁²/2 + gz₁ + q = h₂ + V₂²/2 + gz₂ + w; Carnot efficiency = 1 − T_c/T_h.
- Fluid mechanics: continuity A₁V₁ = A₂V₂; Bernoulli p/ρg + V²/2g + z = constant; Reynolds number Re = ρVD/μ.
- Production: lathe operations, welding types (arc, gas, TIG, MIG), casting defects, and tolerance fits.
- Machine design: factor of safety, stress concentration, fatigue (S–N curve), and standard materials.
Worked example
A steel rod of diameter 20 mm carries a tensile load of 31.4 kN. Find the tensile stress. Reasoning: Area A = πd²/4 = π(0.02)²/4 = 3.14×10⁻⁴ m². Stress σ = P/A = 31,400 / 3.14×10⁻⁴ = 1.0×10⁸ Pa = 100 MPa.
Traps that cost marks
- Using diameter instead of radius in area, or forgetting to convert mm to m.
- Mixing gauge pressure and absolute pressure in thermodynamics.
- Applying Bernoulli across a pump without adding head.
- Confusing orthogonal cutting with oblique cutting in production.