2023 · Q10
The time taken by a train to cross a man travelling in another train is 10 seconds, when the other train is travelling in the opposite direction. However, it takes 20 seconds, if both the trains are travelling in the same direction. The length of the first train is 200 m and that of the second train is 150 m. What is the speed of the first train?
Elementary MathematicsTime, Speed and Distance
- A60 km/hr
- B56 km/hr
- C54 km/hr
- D52 km/hr
Explanation
Crossing a man in the other train covers only the first train's 200 m. In opposite directions (v₁ + v₂) × 10 = 200 gives v₁ + v₂ = 20 m/s; in the same direction (v₁ − v₂) × 20 = 200 gives v₁ − v₂ = 10 m/s. Solving yields v₁ = 15 m/s = 54 km/h (C).