A train crosses a 100 m platform in 30 s at 45 km/h. How long will the same train take to cross a single electric pole? (Find train length first.)

Introduction / Context:
Crossing a platform requires the train to cover its own length plus the platform length. Crossing a pole requires only the train’s own length. We compute the train length from the platform scenario and then find the time for the pole case.

Given Data / Assumptions:

• Platform length = 100 m.
• Speed v = 45 km/h = 12.5 m/s.
• Time over platform = 30 s.

Concept / Approach:
Total distance over platform = (train length + platform length) = v * t. Then train length = (v * t − platform length). For a pole, time = (train length) / v.

Step-by-Step Solution:

Verification / Alternative check:
Check platform case: (275 + 100)/12.5 = 375/12.5 = 30 s, consistent.

Why Other Options Are Wrong:
8 s, 30 s, and 52 s do not match the computed 22 s. Therefore “None of these” is correct here.

Common Pitfalls:
Forgetting that platform adds extra length, or failing to convert km/h to m/s correctly.

Final Answer:
None of these