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Vikas Dangwal

· started a discussion

· 1 Months ago

Wrong solution (Question:109981.0)

Relative speed will be x/a +x/b not x/a -x/b

Question:
Two trains of equal length running at different speed take ‘a’ and ‘b’ second respectively to cross a pole. Then, time taken by the trains to cross each other when they are running in the same direction is :
Options:
A) \(\cfrac{2ab}{a+b}\)
B) \(\cfrac{2n}{a+b}\)
C) \(\cfrac{2ab}{a-b}\)
D) \(\cfrac{a-b}{2ab}\)
Solution:
Ans: (c) Let, length of both the trains = x metres

Then, Speed of the first train \(=\cfrac{x}{a}m/s\)

And, speed of the second train \(=\cfrac{x}{b}m/s\)

We further assume that speed of the second train is more than that of the first train

Total distance = x + x = 2x metres 

Relative speed \(=\cfrac{x}{b}-\cfrac{x}{a}=\cfrac{(a-b)x}{ab}m/s\)

\(\therefore\) Time taken by trains to pass each other 


Knowledge Expert

· commented

· 1 Months ago

Dear student
Given answer is correct
In the Question
Given is the running same direction, that means speed is substract.
and follow the

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