Two trains of equal length, travelling in opposite directions at 54 km/hr and 72 km/hr, cross each other in 10 seconds. In how much time (in seconds) will the first train cross a platform 275 m long?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 30
Trains running in opposite directions cross at the sum of their speeds and together cover both their lengths. A train crossing a platform covers its own length plus the platform.
Relative speed \(=54+72=126\) km/hr \(\displaystyle =126\times\frac{5}{18}=35\) m/s
Sum of lengths \(=35\times10=350\) m, so each train is \(175\) m long
Speed of the first train \(\displaystyle =54\times\frac{5}{18}=15\) m/s
Distance to cross the platform \(=175+275=450\) m
Time \(\displaystyle =\frac{450}{15}=30\) s