RRB JE Mechanical Engineering — Solved Practice Question Bank

Q: A Carnot engine operates between 600K and 300K. Find its efficiency. Sol: η = 1 − T2/T1 = 1 − 300/600 = 1 − 0.5 = 0.5 = 50%. Q: In an Otto cycle, does increasing compression ratio increase or decrease thermal efficiency? Sol: Increases — η = 1 − 1/r^(γ−1), so a higher compression ratio r directly raises efficiency (subject to practical knocking limits). Q: What does the Second Law of Thermodynamics state about heat engines? Sol: No heat engine can convert 100% of absorbed heat into work — some heat must always be rejected to a sink (Kelvin-Planck statement).

Q: Which gear type is self-locking and gives the highest speed reduction in a single stage? Sol: Worm gear — its high friction between worm and worm-wheel makes it self-locking (worm-wheel cannot drive the worm backward), and a single stage can achieve very high reduction ratios. Q: Why do fillets reduce stress concentration at a shaft shoulder compared to a sharp corner? Sol: A fillet provides a gradual change in cross-section, spreading stress lines smoothly, whereas a sharp corner forces stress lines to bunch together abruptly, raising the local stress concentration factor Kt. Q: Which casting process is best suited for producing a small, highly precise, complex-shaped component? Sol: Investment (lost-wax) casting — it achieves the finest surface finish and dimensional accuracy among common casting processes, at higher per-part cost.

Q: Water flows through a pipe that narrows from 20 cm² to 10 cm² cross-section. If velocity in the wider section is 2 m/s, find velocity in the narrower section. Sol: Using continuity A1V1 = A2V2: 20×2 = 10×V2 → V2 = 4 m/s. Q: What principle does a hydraulic jack work on? Sol: Pascal's law — pressure applied at the small piston is transmitted undiminished to the large piston, producing a much larger force output (force = pressure × area, and area is larger at the output piston). Q: A pitot tube is used to measure what quantity in a fluid flow? Sol: Point velocity of flow, via the difference between stagnation pressure and static pressure at that point.