A train passes over a 1 km long bridge. The train’s length is half the bridge length. If it clears the bridge in 2 minutes, what is the train’s speed in km/h?

Introduction / Context:
Passing a bridge requires the train to traverse its own length plus the bridge length. With lengths given and total time known, compute speed from total distance / total time.

Given Data / Assumptions:

• L_bridge = 1000 m; L_train = 500 m (half of 1000 m).
• t = 2 minutes = 120 s.

Concept / Approach:
Total distance S = 1500 m. Speed v(m/s) = S / t. Convert to km/h by multiplying by 3.6.

Step-by-Step Solution:

Verification / Alternative check:
If bridge length doubled, total distance doubles and so does time at fixed speed—relationship remains linear.

Why Other Options Are Wrong:
30 or 50 km/h result from halving/doubling errors; 60 km/h assumes only bridge length or only train length counted.

Common Pitfalls:
Ignoring the train length; mixing seconds and minutes.

Final Answer:
45 km/h