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

Introduction / Context:
When a train passes a platform, the distance covered equals train length + platform length. Convert time to seconds and compute speed = distance/time.

Given Data / Assumptions:

• Train length = 280 m
• Platform length = 3 × 280 = 840 m
• Total covered length = 280 + 840 = 1120 m
• Time = 6 min 40 s = 400 s

Concept / Approach:
Speed (m/s) = total distance (m) / time (s).

Step-by-Step Solution:

Verification / Alternative check:
Units are consistent (m and s). No relative motion adjustments are needed since the platform is stationary.

Why Other Options Are Wrong:
1.4 and 3.2 m/s mismatch 1120/400; “Cannot be determined” is incorrect because all necessary data are provided.

Common Pitfalls:
Forgetting that total distance includes both train and platform lengths, or converting 6 min 40 s incorrectly.

Final Answer:
2.8 m/s.