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psykatic

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## Homework Statement

Two trains A and B, 125m and 100m long respectively are moving in opposite directions on parallel tracks. the velocity of the train B is three times that of train A. The train takes 4s to pass each other, calculate the velocity of each train?

## Homework Equations

Velocity=[tex]\frac {Distance}{Time}[/tex]

## The Attempt at a Solution

Let the velocity of train A be 'v', hence the velocity of the train B would be '3v'.

The relative velocity of train A w.r.t train B = [tex]v_A- v_B[/tex]

=v-(-3v)=4v

*The distance to be covered= 125+100= 225m*Velocity=[tex]\frac{Distance}{Time}[/tex]

Hence, velocity, 4v= [tex]\frac{225}{4}[/tex]

Therefore, 16v=225

Thus, v=14.1

Hence, [tex] v_A[/tex]=14.1 m/s and [tex] v_B[/tex]= 42.3 m/sI've reached the final answer, by using the textual methodology. But the thing which is bothering me is the distance covered, which is given by the addition of the length of both the trains (statement highlighted). Please explain me as to why do we add these lenghts, when the entire train (considering it as a whole, either A or B) moves across the length of the other, and not its own!

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