The speed of a 90 metre long train is 45 km/h. A man is standing right next to the railway line. How much time will the train take to cross him if the speed increases by 20%?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 6.0 second
A man standing by the line is a point, so to pass him the train covers only its own length, 90 m, and the time is length divided by speed. The length is in metres, so the new speed is turned into metres per second, using \(1\) km/h \(=\frac{5}{18}\) m/s.
Speed after the 20% increase: \(45\times1.2=54\) km/h
The same speed in m/s: \(\displaystyle 54\times\frac{5}{18}=15\) m/s
Time to pass the man: \(\displaystyle\frac{90}{15}=6\) seconds