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 <strong>BOTH</strong> 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?
- A. 60 km/hr
- B. 56 km/hr
- C. 54 km/hr ✓
- D. 52 km/hr
Correct Answer: C. 54 km/hr
Explanation
To cross a man, only the length of the first train matters (D = 200 m). Relative speeds: v_1 + v_2 = 200/10 = 20 m/s, and v_1 - v_2 = 200/20 = 10 m/s. Solving gives 2v_1 = 30 \implies v_1 = 15 m/s. In km/hr: 15 \times 18/5 = 54 km/hr.
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