Train–platform crossing time A 200 m train runs at 72 km/h. In how many seconds will it pass a platform 160 m long?

Introduction / Context:
Train-platform problems require summing lengths and handling units carefully. The full clearing requires covering train length plus platform length at constant speed.

Given Data / Assumptions:

• Train length = 200 m.
• Platform length = 160 m.
• Speed = 72 km/h.

Concept / Approach:
Convert speed to m/s, compute total distance to clear, then time = distance / speed.

Step-by-Step Solution:

Verification / Alternative check:
20 m/s * 18 s = 360 m equals the combined length, so the time is consistent.

Why Other Options Are Wrong:
15 s, 20 s, 21 s: Each gives an incorrect product when multiplied by 20 m/s (300 m, 400 m, 420 m), none equals 360 m.

Common Pitfalls:
Using only platform length or failing to convert speed from km/h to m/s.

Final Answer:
18 sec