A train of length $100 m$ travelling at $20{ m }/{ s }$ overtakes another of length $200 m$ travelling at $10{ m }/{ s }$. The time taken by the first train to pass the second train is

When the first train overtakes the second, the relative speed is found by subtracting the slower speed from the faster one, resulting in 20 m/s - 10 m/s = 10 m/s. The total distance that needs to be covered to pass completely is the sum of their lengths, which equals 100 m + 200 m = 300 m. By applying the formula time equals distance divided by relative speed, we get 300 m divided by 10 m/s, which equals 30 s.

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