Question
Two trains of same length are running in parallel tracks
in the same direction with speed 40 km/hr and 70 km/hr respectively. The latter completely crosses the former in 30 seconds. Find the length of each train (in m).Solution
When two trains cross each other, they cover distance equal to the sum of their lengths with relative speed.  Let's take length of each train = x So, total length of both trains = 2x Relative speed = (70 – 40) × (5/18) = 25/3 m/sec. ∴  Total length = Time × Relative speed  ⇒  2x = (30 × 25)/3 ⇒  x = 125 m
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