CDS 2024 · PYQ · Time, Speed and Distance / Trains · medium
Two trains A and B started from stations P and Q respectively towards each other. Train A started at 7 p.m. at a speed of 60 km/hr and train B started at 4 a.m. (next day) at a speed of 90 km/hr. The distance between the two stations P and Q is 800 km. If the lengths of the two trains A and B are 400 m and 500 m respectively, then what is the time taken by them to cross each other?
A.21.6 seconds✓ Correct
B.18.2 seconds
C.17.4 seconds
D.15.4 seconds
Explanation
When two trains moving in opposite directions cross each other, relative speed = 60 + 90 = 150 km/hr = 150 × 5/18 = 125/3 m/s. Total length to cross = 400 + 500 = 900 m. Time = 900 / (125/3) = 900 × 3/125 = 2700/125 = 21.6 seconds.
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