Subject: General Aptitude · Chapter: Problems on Trains · Exam: 2005 · Marks: · Difficulty:
Two trains A and B start running together from the same point in the same direction, at the speeds of 60 kmph and 72 kmph respectively. If the length of each of the trains is 240 metres, how long will it take for train B to cross train A?
(a)1 min 12 secs
(b)1 min 24 secs
(c)2 min 12 secs
(d)2 min 24 secs
Answer
Answer (as printed): D
Explanation
Relative speed $=(72-60) \mathrm{km} / \mathrm{hr}=12 \mathrm{km} / \mathrm{hr}$ $$=\left(12 \times \frac{5}{18}\right) \mathrm{m} / \mathrm{sec}=\left(\frac{10}{3}\right) \mathrm{m} / \mathrm{sec} .$$ Total distance covered = Sum of lengths of trains = (240 + 240) m = 480 m . $$\text { ∴ } \text { Time taken }=\left(480 \times \frac{3}{10}\right) \mathrm{sec}=144 \mathrm{sec}=2 \mathrm{min} 24 \mathrm{sec} .$$