Question

A train $700m$ long is running at $72$ kmph . If it crosses a tunnel in $1$ minute, the length of the tunnel is :

• A. $700m$
• B. $600m$
• C. $550m$
• D. $500m$

Answer 1

The correct option is D $500m$

Length of Train $=700m$
Length of tunnel $=X$ (let)
Time taken to cross the tunnel $=1minute=60sec$
Speed $=72kmph=72\times \frac{5}{18}=20$ m sec.
To cross the tunnel train needs to travel $=$ Length of train $+$ Length of tunnel $=700+x$
Now,
$Speed\times Time=Distance$
$20\times 60=700+x$
$x=1200-700=500$
Length of tunnel $=500m$