Quick-Revision Formula & Fact Capsules

This chapter condenses the most frequently tested formulas and one-line facts for last-minute revision.

8A.1 Mechanics & Strength of Materials

Newton's Second Law: F = ma. Hooke's Law: σ = Eε. Steel's E: ~2×10⁵ N/mm² (200 GPa). Poisson's Ratio (metals): ~0.25–0.35. FoS = Ultimate/Yield strength ÷ Working stress.

8A.2 Thermodynamics

First Law: ΔU = Q − W. Carnot efficiency: η = 1 − (T_L/T_H). Otto cycle: SI engines, constant-volume heat addition. Diesel cycle: CI engines, constant-pressure heat addition. Rankine cycle: steam power plants.

8A.3 Theory of Machines

Four-bar mechanism: 4 links. Flywheel: smooths instantaneous speed fluctuations. Governor: regulates mean speed over varying load. Worm gear: high reduction, often self-locking.

8A.4 Fluid Mechanics

Water density: 1000 kg/m³. Laminar flow: Re < ~2000. Turbulent flow: Re > ~4000. Pelton wheel: impulse, high head/low flow. Francis turbine: reaction, medium head/flow. Kaplan turbine: reaction, low head/high flow.

8A.5 Manufacturing

Vernier caliper least count: ~0.02mm. Micrometer least count: ~0.01mm. Sand casting: most versatile/common. Investment casting: highest accuracy/detail.

8A.6 IC Engines

Four-stroke: 1 power stroke per 2 revolutions. Two-stroke: 1 power stroke per 1 revolution. SI engine: Otto cycle. CI engine: Diesel cycle.

8A.7 Exam Pattern

RRB JE negative marking: 1/3 mark. CBT 2 Technical Abilities: ~100 marks.

8A.8 Practice Set — Formula Capsules (14 MCQs)

1. Newton's Second Law is expressed as:
   (a) F = ma (b) F = m/a (c) F = m+a (d) F = a/m
2. Hooke's Law is expressed as:
   (a) σ = Eε (b) σ = E/ε (c) σ = E+ε (d) σ = ε/E
3. The Carnot cycle efficiency formula is:
   (a) η = 1 − (T_L/T_H) (b) η = T_L/T_H (c) η = T_H/T_L (d) η = 1 + (T_L/T_H)
4. A four-bar mechanism has how many links?
   (a) Two (b) Three (c) Four (d) Six
5. Laminar pipe flow is generally associated with Reynolds Numbers:
   (a) Below ~2000 (b) Above ~4000 (c) Exactly 3000 (d) Above 10,000
6. A Pelton wheel is best suited for:
   (a) Low head, high flow (b) High head, low flow (c) Zero head (d) Compressed air only
7. A vernier caliper's typical least count is approximately:
   (a) 0.02mm (b) 0.2mm (c) 2mm (d) 20mm
8. A four-stroke engine completes one power stroke per:
   (a) One crankshaft revolution (b) Two crankshaft revolutions (c) Four revolutions (d) Half a revolution
9. RRB JE examinations apply negative marking of:
   (a) 1/4 mark (b) 1/3 mark (c) 1/2 mark (d) None
10. Steel's Modulus of Elasticity is approximately:
    (a) 2×10⁵ N/mm² (b) 25 GPa (c) 2×10² N/mm² (d) 9.81 kN/m³
11. The Otto cycle applies to which type of engine?
    (a) CI (diesel) (b) SI (petrol) (c) Steam turbines (d) Gas compressors only
12. A governor's primary function is to:
    (a) Store kinetic energy for one cycle only (b) Regulate mean engine speed over varying load (c) Provide gear reduction (d) Measure temperature
13. A micrometer's typical least count is approximately:
    (a) 0.1mm (b) 0.01mm (c) 1mm (d) 10mm
14. Poisson's Ratio for common metals typically ranges between:
    (a) 0.05–0.10 (b) 0.25–0.35 (c) 0.50–0.75 (d) 1.0–1.5

Answer Key

1.(a)

2.(a)

3.(a)

4.(c)

5.(a)

6.(b)

7.(a)

8.(b)

9.(b)

10.(a)

11.(b)

12.(b)

13.(b) 14.(b)