When two bodies move in the same direction, their relative speed is the difference of their individual speeds ⇒ Relative speed of train & man = 58 – 4 = 54 km/hr. = 54 × 5/18 = 15 m/sec. ∵ Time taken to cross the running man = Length of train/Speed of train ⇒ Time taken to cross the running man = 150/15 = 10 sec.