Correct Answer - Option 4 : 6 seconds
Given:
A 120m long train crosses a 280m long tunnel in 20 seconds.
Formula Used:
Time = [ L1 + L2] / Relative speed
Where, L1 = length of train; L2 = length of object that train is crossing
Relative Speed (RS) = Speed of train + speed of platform(= 0)
Calculation:
20 seconds = [120 + 280]/RS
⇒ 20 seconds = [120 + 280]/Speed of train [∵ speed of platform = 0]
⇒ Speed of train = 400/20 = 20 m/s
Now, time taken by train to cross the pole = Distance/Speed
Also, length of pole = 0 and speed of pole = 0
⇒ Time taken by train to cross the pole = Length of train / Speed of train
= 120/20 = 6 seconds
