Correct Answer - Option 1 : 30 seconds
A 130 m long train crosses a pole in 20 seconds
Time = Distance/ Speed
Since Time = Distance/ Speed = [Length of train + Length of pole]/Relative Speed and Length of pole = 0
And Relative Speed (RS) = Speed of train + Speed of pole and Speed of pole = 0
RS = Speed of train.
Time = Length of train/Relative Speed
⇒ 20 = 130/Speed of train
⇒ Speed of train = 6.5 m/s
Time taken by the train to cover a distance of 195 m = Distance/Speed
⇒195/6.5 = 30 seconds
∴ Time taken by the train to cover a distance of 195 m is 30 sec.
When it is asked for the time required to cover a certain distance we have to ignore the length of the object which is covering the distance during calculation.
We should not confuse with "Time required to cover anothe object of certain length", in this case we will take total distance cover = Sum of length of the object and the length of the object which is crossing the other.