Tunnel length from crossing time A train 700 m long runs at 72 km/h and crosses a tunnel completely in 1 minute. What is the length of the tunnel?

Introduction / Context:
Tunnel problems require adding the tunnel length to the train length for total distance covered during the crossing interval. Uniform motion assumptions apply.

Given Data / Assumptions:

• Train length = 700 m.
• Speed = 72 km/h = 20 m/s.
• Time t = 60 s.

Concept / Approach:
Compute total distance in the given time, then subtract the train length to isolate the tunnel length.

Step-by-Step Solution:

Verification / Alternative check:
Recompose: 700 + 500 = 1200 m in 60 s at 20 m/s. This checks out.

Why Other Options Are Wrong:
700 m, 600 m, 550 m: All give totals different from 1200 m in 60 s at 20 m/s.

Common Pitfalls:
Using only tunnel length in D = v * t; you must include the whole train length during clearing.

Final Answer:
500 m