A train 850 m long is running at a speed of 70 km/h. If it crosses a tunnel in \(1\frac{1}{2}\) minutes, then the length of the tunnel (in m) is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 900
To cross a tunnel, the train must travel the length of the tunnel plus its own length: the engine enters the tunnel, and the crossing ends only when the last coach leaves it.
Speed: \(\displaystyle 70\times\frac{5}{18}=\frac{175}{9}\) m/s
Time: \(1\frac{1}{2}\) minutes \(=90\) s
Distance covered: \(\displaystyle \frac{175}{9}\times90=1750\) m
Length of the tunnel: \(1750-850=900\) m