A train 800 metres long is running at a speed of 78 km hr If it crosses a tunnel in 1 minute then th......

A train 800 metres long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel (in meters) is :

Speed =[ 78 x ( 5/18 ) ] m/sec = 65/3 m/sec.

Time = 1 minute = 60 sec.

Let the length of the tunnel be x metres.

Then, [ (800 + x )/ 60 ]= 65/3

3(800 + x) = 3900

 x = 500.

Hence, option 3 is the correct answer.

By: Amit Kumar