A 360 m long train is moving at a speed of 44 km/h. In how much time (in seconds) will it completely cross a 140 m long bridge?

Introduction / Context:
This is a classic time and distance problem involving a train crossing a bridge. When a train crosses a bridge, it must cover not only its own length but also the full length of the bridge. The question checks your understanding of effective distance, speed conversion from km/h to m/s, and the use of the basic distance formula. Such questions are very common in railway and aptitude examinations.

Given Data / Assumptions:
- Length of the train = 360 m.
- Length of the bridge = 140 m.
- Speed of the train = 44 km/h, assumed constant.
- The train moves in a straight line with no acceleration or deceleration.
- We need the total time taken for the train to completely clear the bridge, expressed in seconds.

Concept / Approach:
Two main ideas are used here:
- Effective distance to be covered while crossing a bridge = length of train + length of bridge.
- Relationship between distance, speed, and time: distance = speed * time.
Because the lengths are given in metres and the answer is required in seconds, we must convert the speed from km/h to m/s using the standard factor: 1 km/h = (5/18) m/s.

Step-by-Step Solution:
Step 1: Compute the effective distance.Effective distance = 360 m + 140 m = 500 m.Step 2: Convert the speed from km/h to m/s.Speed in m/s = 44 * (5/18) = 220/18 m/s ≈ 12.22 m/s.Step 3: Use the formula time = distance / speed.Time = 500 / (220/18) = 500 * 18 / 220 = (500/220) * 18.Simplify: 500/220 = 50/22 = 25/11. So time = (25/11) * 18 = 450/11 seconds ≈ 40.91 seconds.Step 4: Round to the nearest whole second, which is 41 seconds.

Verification / Alternative check:
An approximate mental check can be done. If the train moves at about 12 m/s, then in 40 seconds it would cover roughly 480 m, and in 41 seconds it would cover about 492 m. Because the exact calculation gave slightly more than 40.9 seconds and the required distance is 500 m, rounding to 41 seconds is reasonable and consistent. This matches option “41 seconds”.

Why Other Options Are Wrong:
- 36 seconds and 39 seconds are too small; at roughly 12 m/s, they would cover only about 432 m or 468 m, which is less than 500 m.
- 43 seconds is slightly larger than required and would correspond to covering more distance than necessary at the given speed.
Only 41 seconds matches the computed and rounded value correctly.

Common Pitfalls:
Candidates sometimes forget to add the length of the bridge to the length of the train and use only the train length as distance. Another frequent mistake is to mix kilometres and metres or hours and seconds without converting units, leading to incorrect answers. Always make sure to convert speed to m/s when distances are in metres and time is required in seconds.

Final Answer:
The train will cross the bridge completely in 41 seconds.