Quick Theory Review

Measurement is the process of assigning numbers to physical quantities. The International System of Units (SI) is the modern metric system used in science, engineering and railways. It has seven base units: metre (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for current, kelvin (K) for temperature, mole (mol) for amount of substance and candela (cd) for luminous intensity.

Indian Railways uses both SI and CGS units depending on the context. Distance is measured in kilometres, speed in km/h, axle load in tonnes, rail length in metres, and current in amperes. Prefixes like kilo (10³), mega (10⁶), centi (10⁻²), milli (10⁻³) and micro (10⁻⁶) are added to base units to form multiples or sub-multiples. Always convert all quantities to the same system before solving numerical problems.

Practice MCQs

Easy (1–8)

1. 1 km equals
   A) 100 m
   B) 1000 m
   C) 10000 m
   D) 500 m

   Answer

   Correct: Option B. 1 km = 1000 m.

2. The SI unit of mass is
   A) gram
   B) pound
   C) kilogram
   D) quintal

   Answer

   Correct: Option C. kilogram is the SI base unit.

3. Which of these is the smallest?
   A) 1 mm
   B) 1 cm
   C) 1 m
   D) 1 km

   Answer

   Correct: Option A. 1 mm = 0.1 cm.

4. 1 hour =
   A) 60 s
   B) 360 s
   C) 3600 s
   D) 1000 s

   Answer

   Correct: Option C. 60 × 60 = 3600 s.

5. The prefix “mega” stands for
   A) 10³
   B) 10⁶
   C) 10⁻³
   D) 10⁻⁶

   Answer

   Correct: Option B. mega = million = 10⁶.

6. Which unit is used to express train speed in India?
   A) m/s
   B) km/h
   C) miles/h
   D) ft/s

   Answer

   Correct: Option B. Indian Railways uses km/h.

7. 1 tonne =
   A) 100 kg
   B) 1000 kg
   C) 10 quintal
   D) 100 quintal

   Answer

   Correct: Option B. 1 tonne = 1000 kg.

8. The SI unit of electric current is
   A) volt
   B) ohm
   C) ampere
   D) watt

   Answer

   Correct: Option C. ampere (A).

Medium (9–17)

9. A train travels 180 km in 3 h. Its speed in m/s is
   A) 15 m/s
   B) 16.66 m/s
   C) 20 m/s
   D) 50 m/s

   Answer

   Correct: Option B. 180 km = 180000 m; 3 h = 10800 s; 180000/10800 ≈ 16.66 m/s.

10. How many millimetres are in 0.025 km?
    A) 25000
    B) 2500
    C) 250000
    D) 250

    Answer

    Correct: Option A. 0.025 km = 25 m = 25000 mm.

11. 1 horsepower (HP) equals approximately
    A) 746 W
    B) 746 kW
    C) 1000 W
    D) 550 W

    Answer

    Correct: Option A. 1 HP ≈ 746 watt.

12. The density of rail steel is 7.8 g/cm³. In kg/m³ it is
    A) 78
    B) 780
    C) 7800
    D) 78000

    Answer

    Correct: Option C. 7.8 g/cm³ = 7.8 × 1000 kg/m³ = 7800 kg/m³.

13. Which one is NOT a unit of energy?
    A) joule
    B) calorie
    C) kilowatt
    D) kilowatt-hour

    Answer

    Correct: Option C. kilowatt is power, not energy.

14. 1 nautical mile is about
    A) 1.151 km
    B) 1.852 km
    C) 1.609 km
    D) 2.0 km

    Answer

    Correct: Option B. 1 nautical mile = 1.852 km.

15. The acceleration due to gravity (g) is taken as
    A) 9.8 m/s²
    B) 98 m/s²
    C) 0.98 m/s²
    D) 0.098 m/s²

    Answer

    Correct: Option A. standard g = 9.8 m/s².

16. 1 bar equals
    A) 10⁵ Pa
    B) 10³ Pa
    C) 10⁶ Pa
    D) 10⁴ Pa

    Answer

    Correct: Option A. 1 bar = 10⁵ pascal.

17. If an axle load is 22.5 t, its weight in kN is about (g = 10 m/s²)
    A) 225 kN
    B) 22.5 kN
    C) 2.25 kN
    D) 2250 kN

    Answer

    Correct: Option A. 22.5 t = 22500 kg; W = mg = 22500 × 10 = 225000 N = 225 kN.

Hard (18–25)

18. A 1.5 km long goods train passes a pole in 90 s. Its speed in km/h is
    A) 54
    B) 60
    C) 72
    D) 90

    Answer

    Correct: Option B. speed = 1.5 km / (90/3600) h = 60 km/h.

19. 1 slug (Imperial unit of mass) ≈ 14.59 kg. The weight of 1 slug on Earth is
    A) 1.459 N
    B) 14.59 N
    C) 143 N
    D) 1430 N

    Answer

    Correct: Option C. W = 14.59 × 9.8 ≈ 143 N.

20. The unit “knot” measures speed in
    A) km/h
    B) nautical miles per hour
    C) miles per hour
    D) ft/s

    Answer

    Correct: Option B. 1 knot = 1 nautical mile per hour.

21. A loco traction motor draws 600 A at 750 V for 2 h. Energy consumed in kWh is
    A) 450
    B) 900
    C) 1200
    D) 1500

    Answer

    Correct: Option B. P = VI = 750 × 600 = 450 kW; E = 450 kW × 2 h = 900 kWh.

22. Convert 5 m/s² into km/h².
    A) 50
    B) 500
    C) 18000
    D) 64800

    Answer

    Correct: Option D. 5 m/s² = 5 × (1/1000 km)/(1/3600 h)² = 5 × 3600²/1000 = 64800 km/h².

23. 1 dyne =
    A) 10⁻³ N
    B) 10⁻⁵ N
    C) 10⁻⁷ N
    D) 10⁵ N

    Answer

    Correct: Option B. 1 dyne = 1 g·cm/s² = 10⁻⁵ kg·m/s² = 10⁻⁵ N.

24. The angular frequency of 50 Hz AC in rad/s is
    A) 50
    B) 100
    C) 314
    D) 157

    Answer

    Correct: Option C. ω = 2πf = 2 × 3.14 × 50 ≈ 314 rad/s.

25. A 60 kg rail piece is lifted 1.2 m in 4 s. The minimum power required in watts is (g = 10 m/s²)
    A) 18
    B) 72
    C) 180
    D) 720

    Answer

    Correct: Option C. Work = mgh = 60 × 10 × 1.2 = 720 J; P = 720 J / 4 s = 180 W.

Quick Shortcuts & Tips

1. km/h → m/s: multiply by 5/18
   m/s → km/h: multiply by 18/5
2. HP → kW: 1 HP ≈ 0.75 kW (746 W)
3. tonne → kg: add three zeroes (1 t = 1000 kg)
4. kWh → joule: 1 kWh = 3.6 × 10⁶ J
5. Always write units in the final answer—railway exams deduct ¼ mark for missing units.