Two trains and of length and are travelling into a tunnel of length in parallel tracks from opposite directions with velocities 108 km/h and 72 km/h, respectively. If train ‘A’ takes 35 s less time than train ‘B’ to cross the tunnel then, length ‘L’

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Solution

Q.
Two trains $‘ A ’$ and $‘ B ’$ of length $' l'$ and $' 4 l'$ are travelling into a tunnel of length $' L'$ in parallel tracks from opposite directions with velocities 108 km/h and 72 km/h, respectively. If train ‘A’ takes 35 s less time than train ‘B’ to cross the tunnel then, length ‘L’ of tunnel is: (Given L = 60 $l$ ) [2023]

1 1200 m

2 2700 m

3 1800 m

4 900 m

Ans.
(3)

$\frac{60 ℓ + 4 ℓ}{20} - \frac{61 ℓ}{30} = 35$

$\Rightarrow ℓ = \frac{1050}{35}$

$\Rightarrow L = 60 ℓ = \frac{1050}{35} \times 60 = 1800 m$

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