Question

Two trains 120m and 80min length are running in opposite direction with velocity 42km/hr and 30km/hr.in what time they will completely cross each other

Answer 1

relative velocity =42+30=72 km/hr *5/18=20 m/s
total distance = 200m
time=distance/ speed =200/20=10 sec

Answer 2

Time = Relative Displacement / Relative Velocity
= (120 m + 80 m) / [(42 kmph + 30 kmph) × 5/18 (m/s)/kmph]
= 10 seconds

It takes 10 seconds to completely cross each other.