Question

100 m long train crosses 400 m bridge with velocity 72km/ h. find time to cross the bridge

Answer 1

Distance = 400 + 100 = 500m
Speed = 72 km/hr = 72 X 5/18 = 20m/s

Time = Distance/speed = 500m/20m/s = 25s

It 25 second

Answer 2

Distance
= 400 +  100 
= 500m 
Speed
= 72 km/hr
= 72 X 5/18
= 20m/s

Time = Distance/speed
= 500m/20m/s
= 25s

Your answer is 25 seconds......