Speed of train in m/sec = (speed of train in km/hr) x 5/18
∴ speed of train in m/sec = 54 x 5/18 = 15 m/sec
Time taken to cross the tunnel = 2 minutes = 120 sec
Therefore, Total length covered by train in crossing the tunnel = Speed of train x Time taken to cross the tunnel
= 15 m/sec x 120 sec = 1800 m
Now, we know that
Total length covered by train in crossing the tunnel = Length of train + Length of tunnel
Given, Length of train =400m and
Calculated above, Length covered by train in crossing the tunnel = 1800 m
Therefore, Length of tunnel = 1800m- 400m = 1400m
