A 350 m long train is moving at 20 km/h. A man is walking toward the train from the opposite direction at 1 km/h (treat the man as a point). In how many seconds will the train completely cross the man?

Introduction / Context:When two bodies move toward each other, their relative speed is the sum of individual speeds. For a point-like man and a finite-length train, the crossing time equals (train length) / (relative speed).

Given Data / Assumptions:

• Train length = 350 m.
• Train speed = 20 km/h.
• Man speed (opposite) = 1 km/h.
• 1 km/h = 1000/3600 m/s.

Concept / Approach:Compute relative speed in m/s, then use time = distance / speed. Only the train’s length matters because the man is a point object.

Step-by-Step Solution:

Verification / Alternative check:Multiply 60 s by 5.833... m/s ≈ 350 m, matching the train length.

Why Other Options Are Wrong:27/35/45 s correspond to higher relative speeds that are not possible with the given velocities.

Common Pitfalls:Forgetting to add speeds for opposite motion, or not converting km/h to m/s before dividing.

Final Answer:60 sec