A train 300 m long takes 15 seconds to cross a man who is walking in the same direction at 6 km/hr. What is the speed of the train?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 78 km/hr
To cross a man, the train covers its own length. When both move in the same direction, the train gains on the man at the difference of their speeds.
Relative speed \(\displaystyle =\frac{300}{15}=20\) m/s
In km/hr: \(\displaystyle 20\times\frac{18}{5}=72\) km/hr
Speed of the train \(-\,6=72\), so speed of the train \(=72+6=78\) km/hr