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.