A 280 m long train crosses a platform that is three times its own length in 6 min 40 s. What is the speed of the train (in m/s)?

Introduction / Context:
Crossing a platform requires the train to travel the sum of its own length and the platform length. The speed follows directly from total distance over total time, provided all units are consistent.

Given Data / Assumptions:

• Train length = 280 m.
• Platform length = 3 * 280 = 840 m.
• Total time = 6 min 40 s = 6 * 60 + 40 = 400 s.

Concept / Approach:
Total distance to clear platform = 280 + 840 = 1120 m. Speed v = distance / time in m/s because distance is in meters and time in seconds.

Step-by-Step Solution:

Verification / Alternative check:
If v = 2.8 m/s, time required for 1120 m is 1120/2.8 = 400 s, which matches 6 min 40 s.

Why Other Options Are Wrong:
1.4 m/s or 3.2 m/s produce times inconsistent with 400 s; “Cannot be determined” is false because sufficient data are given.

Common Pitfalls:
Forgetting to multiply platform length correctly or converting the time from minutes and seconds.

Final Answer:
2.8 m/s