A train runs at 45 km/h and takes 12 seconds to pass a fixed point. What is the length of the train (in meters)?

Introduction / Context:
Passing a fixed point means the train covers a distance equal to its own length in the given time. Speed–time–distance relations in consistent units yield the length.

Given Data / Assumptions:

• Speed = 45 km/h.
• Time to pass a point = 12 s.

Concept / Approach:
Convert speed to m/s, multiply by time to get distance (which equals train length).

Step-by-Step Solution:
45 km/h = 45 * (1000/3600) = 12.5 m/s.Length L = 12.5 * 12 = 150 m.

Verification / Alternative check:
If L = 150 m and speed is 12.5 m/s, time = L / v = 150 / 12.5 = 12 s, matching the data.

Why Other Options Are Wrong:
90 or 120 m underestimate the product; 540 m is far too large given the moderate speed and short time.

Common Pitfalls:
Leaving speed in km/h when time is in seconds, or using 360 instead of 3600 in conversions.

Final Answer:
150 meters