Correct Answer - Option 1 : 80 km / hr
Given:
Length of two trains are 120 m and 130 m respectively.
They crosses each other in 6 sec.
Speed of first train = 70 km / hr.
Formula:
If speed of the two trains be x km / hr and y km / hr respectively, if x > y.
Relative speed, if opposite directions = (x + y) km / hr
1 km / hr = (5 / 18) m / s
Calculation:
Let speed of second train be x km / hr, then
Relative speed of train = (70 + x) km / hr
According to the question
(70 + x) × (5 / 18) = (130 + 120) / 6
⇒ (70 + x) = (250 / 6) × (18 / 5)
⇒ (70 + x) = 50 × 3
⇒ x = 150 - 70
⇒ x = 80 km / hr
∴ Speed of second train is 80 km / hr.