A 150 metre long train crosses a 500 metre long bridge in 30 seconds. What time will it take to cross a platform 370 metre long?

Appeared in: RRB Staff Nurse Delhi-2015

Explanation

The core principle is that the total distance a train covers when crossing an object is the sum of its own length and the object's length.
First, calculate the train's speed using the bridge-crossing data: Speed = (150m + 500m) / 30s = 650m / 30s = 65/3 m/s.
Next, calculate the total distance to cross the platform: 150m (train) + 370m (platform) = 520m.
Finally, use the train's speed to find the time to cross the platform: Time = Distance / Speed = 520m / (65/3 m/s) = 24 seconds.

Option A: This is an incorrect calculation. It does not result from correctly applying the speed and distance formulas to the given values.
Option B: This is the time taken to cross the 500m bridge, not the 370m platform. Since the platform is shorter than the bridge, the time taken to cross it must also be shorter.
Option D: This result indicates a calculation error, possibly by using an incorrect distance or speed. For instance, only considering the platform's length (370m) and forgetting the train's length would lead to an incorrect, shorter time.

Visual 1: Diagram - An infographic illustrating the concept of total distance. It would show the train at the point of entering the platform and at the point where its rear has just left the platform, with the total distance marked as 'Length of Train + Length of Platform'.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Time, Speed, and Distance as background academic context rather than a clinical decision trigger.
This question tests quantitative aptitude and logical reasoning, which are essential skills for nurses.
Nurses frequently perform calculations for medication dosages, IV drip rates, and fluid balances, all of which require accuracy and a strong understanding of mathematical principles.
What if the train's speed was given in km/h? You would first need to convert the speed to m/s (by multiplying by 5/18) before proceeding with the calculations to ensure all units are consistent.

How to Approach the Question

First, identify all the known values provided in the problem: length of the train, length of the bridge, time to cross the bridge, and length of the platform.
Recognize that this is a two-part problem. The information from the first scenario (crossing the bridge) must be used to find a value (speed) that can be applied to the second scenario (crossing the platform).
Remember the key formula for this type of problem: Total Distance = Length of Train + Length of Object (Bridge/Platform).
Step 1: Calculate the train's speed using the formula Speed = Total Distance / Time for the bridge scenario.
Step 2: Calculate the new total distance for the platform scenario.
Step 3: Use the speed from Step 1 and the distance from Step 2 to calculate the final answer using the formula Time = Total Distance / Speed.

Concept Tested & Keywords

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Practise the full RRB Staff Nurse Delhi-2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.