Correct Answer - Option 1 : 78 sec
Given
Train crosses a platform of 200 m long in 90 seconds
Speed of train = 60 km/hr.
Concept
Speed = (Distance/Time)
Speed in meter/second = (5/18) km/h
When a train cross a pole it means the length of train is actual distance.
Calculation
Let the length of train be x meter
Total distance covered by train = length of train + length of platform
⇒ Total distance covered by train = (x + 200) m.
⇒ Speed of train in meter per second = (5/18) × 60
⇒ Speed of train in meter per second = (50/3) m/s
⇒ (50/3) = (x + 200)/90
⇒ (50 × 90)/3 = x + 200
⇒ 1500 = x + 200
⇒ x = 1500 - 200
⇒ x = 1300 meter
Length of train = 1300 meter
Now,
⇒ The time taken by the train to cross an electric pole = (1300/(50/3))
⇒ The time taken by the train to cross an electric pole = 78 sec.
∴ The time taken by the train to cross an electric pole is 78 sec.
