Total distance covered when two trains cross each other = Length of Train 1 + Length of Train 2 Relative speed when two trains move in opposite directions = Speed of Train 1 + Speed of Train 2 Distance = Speed × Time Calculation: Relative speed =60km∕h+110km∕h=170km∕h ⇒ Relative speed in m/s =170×(1000∕3600)=170×(5∕18)m∕s ⇒ Total distance covered = Relative speed × Time =170×(5∕18)m∕s×21≈991.66m ⇒ Length of Train 2 = Total distance covered - Length of Train 1 ⇒ Length of Train 2=991.66−360≈631.66m