Question

A train 700 m long is running at the speed of 72 km per hour if it crosses a tunnel in 1 minutes then the length of the tunnel in metres is

Answer 1

Let length of the tunnel be x.

The train is travelling at 72 km/h.

We know that 1km = 1000m and 1h = 3600s

Hence, speed in m/s = (72 × 1000) / (3600) = 20 m/s

Hence, the train covers 20m every second.

When the front portion of the train is at the start of the tunnel, the back portion is still 700m behind (as the length of the train is 700m).

Hence, time taken to cover (x + 700m) = 1 minute.

Distance covered in 1 minute = distance covered in 1 s × 60 = 20 × 60 = 1200 m

Hence, x + 700 = 1200

Therefore, x = 500m

Answer 2

 the length of the tunnel be x mt. 

Speed of the train = 72 kmph = 72×5/18= 20 m/sec.

when Train crosses the tunnel in 60 sec. 

Therefore, (700+x)20=60(700+x)20=60

(i.e) Time taken to cover (700+x)(700+x) 

(700+x)(700+x) = 60×20
ans.


700 + x = 1200 

x = 1200 - 700 = 500 mts.