A train 800 metres long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel (in meters) is:

Given Data

• Train length = 800 m
• Speed of train = 78 km/hr
• Time to clear the tunnel = 1 minute = 60 s

Step 1: Convert speed to m/s
1 km/hr = 5/18 m/s Speed = 78 × (5/18) = 21.666... m/s

Step 2: Total distance covered while clearing the tunnel
Distance = Speed × Time = 21.666... × 60 = 1300 m

Step 3: Extract tunnel length
Total distance = Train length + Tunnel length Tunnel length = 1300 − 800 = 500 m

Final Answer
The length of the tunnel is 500 m.