Correct Answer - Option 3 : 960 m

Given:

Speed of the train = 72 km/h

Length of the train = 240 m

Time to cross a tunnel = 1 minute

Concept used:

Distance = Speed × Time

km/h × 5/18 = m/sec

1 minute = 60 sec

Calculation:

Speed of the train = 72 km/h

⇒ 72 × 5/18 = 20 m/sec

Time to cross the tunnel = 60 sec

Let the length of the tunnel be L.

(240 + L)/20 = 60

⇒ (240 + L) = 60 × 20

⇒ 240 + L = 1200

⇒ L = 1200 – 240

⇒ L = 960

∴ The length of the tunnel is 960 m.