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:

Given Data

• Train length = 125 m
• Man runs at 5 km/hr in the same direction
• Time to pass the man = 10 s
• Required: train speed

Step 1: Relative speed with the manRelative speed = (v − 5) km/hr = (v − 5) × (5/18) m/sWhen passing a man, distance = train length = 125 m125 = 10 × (v − 5) × (5/18)(v − 5) = 12.5 × (18/5) = 45v = 45 + 5 = 50 km/hr

Checks & Common Pitfalls

• Same direction ⇒ subtract speeds.
• Distance equals the train length when passing a person.

Final AnswerThe train speed is 50 km/hr.