IIM Ahemdabad Interview Question - Train+Tunnel
A train enters a tunnel and takes 2 minutes to pass through it. If the train is 500m long, what is the speed?
This is not just a maths question — it’s a question to test your attention to details. Let's solve it step by step.
The Explained Step by Step Solution
Let’s assume:
Length of the train = 500 meters
Time taken to completely pass the tunnel = 120 seconds = 2 minutes
Let’s say the length of the tunnel is L meters
Let’s say the speed of the train is S m/s
Important Note
To completely clear the tunnel the whole train must not be in the tunnel, in other words, it has to cover a total distance of:
Distance = Length of the train + Length of the tunnel = 500 + L
But we don't know L yet. This is where the trick is.
However , if in 120 seconds the total distance traveled is (500 + L), this was supposed to help us find speed, so we are stuck — unless the question allowed the total distance (and thus total time), or asked in another way, to find actual total distance.
Now let's assume the length of the tunnel = 500 Meters
Updated Detail:
Length of the train = 500 meters
Length of tunnel = 500 meters
Total distance covered = 500 + 500 = 1000 meters
Time = 2 minutes = 120 seconds
Speed Calculation
Speed (m/s) = Distance / Time
= 1000 / 120
= 8.33 m/s
Now convert to km/h:
1 m/s = 3.6 km/h
So:
8.33 × 3.6 = 29.99 km/h ≈ 30 km/h
The FInal Answer -
The final answer is 30 km/h.