Question

What is the length of a running train crossing another 180 metre long train running in the opposite direction?
I. The relative speed of the two trains was 150 kmph.
II. The trains took 9 seconds to cross each other.

• A. I alone sufficient while II alone not sufficient to answer
• B. II alone sufficient while I alone not sufficient to answer
• C. Either I or II alone sufficient to answer
• D. Both I and II are not sufficient to answer
• E. Both I and II are necessary to answer

Answer 1

The correct option is E Both I and II are necessary to answer

Let the two trains of length a metres and b metres be moving in opposite directions at u m/s and v m/s.

Time taken to cross each other $=\frac{(a+b)}{(u+v)}sec.$

Now, $b=180,u+v(150\times \frac{5}{18})m/sec=\frac{125}{3}m/sec.$

$\Rightarrow 9=\frac{a+180}{\left(125/3\right)}$

$\Rightarrow a=(375-180)=195m$