A train 125 m long passes a man, running at 5 km/hr in the same direction in…
2025
A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is:
- A.
45 km/hr
- B.
50 km/hr
- C.
54 km/hr
- D.
55 km/hr
Attempted by 16 students.
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Correct answer: B
Solution: Find the train's speed.
Compute the relative speed of the train with respect to the man: relative speed = length ÷ time = 125 m ÷ 10 s = 12.5 m/s (which is 25/2 m/s).
Convert 12.5 m/s to km/hr: 12.5 × 18/5 = 45 km/hr. This is the speed of the train relative to the man.
Add the man's speed (5 km/hr) to the relative speed to get the train's actual speed: 45 + 5 = 50 km/hr.
Alternative algebraic method: Let train speed = x km/hr. Relative speed = (x − 5) km/hr = (x − 5) × 5/18 m/s. Using 125 ÷ ((x − 5) × 5/18) = 10 and solving yields x = 50 km/hr.