Two trains are traveling at speeds of 90 and 60 kilometers per hour, respectively. They are 1.10 kilometers and 0.9 km long, respectively. The duration in seconds needed for the slower train to pass the quicker train is

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answer is C.

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Detailed Solution

Concept: The relative speeds of the trains must first be determined. The distance that the slower train must travel to pass the quicker train. Then we must calculate time using the speed, distance, and time formula.
A moving object's relative speed is its velocity in relation to another. Relative speed is determined by subtracting the speeds of two objects moving in the same direction. The relative speed is calculated by summing the two speeds when the two objects are traveling in opposing directions.
Relative speed between trains:

Now, changing the speed from

we get,

The slower train must now travel 2 kilometers

to pass the quicker train.

is the time in seconds it takes for a slower train to pass a quicker train.
From the notations above,

As a result, 48 seconds are needed for the slower train to pass the quicker train.
Hence, option 3 is correct.

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