Problems on Trains – Speed from time to pass a standing man: A train 300 m long passes a stationary man in 15 seconds. What is the speed of the train?

Introduction / Context:The distance covered while passing a standing man is simply the train’s own length. Use speed = distance / time, then convert to km/h if required.

Given Data / Assumptions:

• L_train = 300 m.
• Time = 15 s.
• Man is stationary (speed = 0).

Concept / Approach:Speed (m/s) = 300 / 15 = 20 m/s. Convert to km/h by multiplying by 3.6.

Step-by-Step Solution:Speed = 20 m/s = 20 * 3.6 = 72 km/h.

Verification / Alternative check:At 72 km/h (20 m/s), 15 s * 20 m/s = 300 m, consistent with the train length.

Why Other Options Are Wrong:40, 50, 54, 60 km/h correspond to speeds that would not cover 300 m in 15 s.

Common Pitfalls:Using 3.8 or 3.2 as the conversion factor; inverting the conversion accidentally.

Final Answer:72 km/hr