Explanation
Speed of the two trains: 60 km/hr and 90 km/hr
If train cross each other, then effective speed = 60 + 90 = 150 km/hr
Length of first train = 1.10 km or 1100 m
Length of second train = 0.9 km or = 900 m
formula
Speed = Distance/Time
⇒ 150 × (5/18) = 2000/Time
⇒ 125/3 = 2000/Time
⇒ Time = 2000 × (3/125)
∴ Time = 48 seconds.
Relative speed = 60 + 90 = 150 km/hr. = 150 x 5/18 = 125/3 m/sec. Distance covered = 1.10 + 0.9 = 2 km = 2000 m. Required time = 2000 x 3/125 = 48 sec.