Dear student,
we will see how much distance train must cover.
First, the first point of the train( which is the engine) crosses the bridge, so distance travelled is the length of the bridge 400m. To completely cross the bridge, the last point of the train must also cross the bridge. For this, the train must travel the length of the train, which is 200m.
So, total distance covered by the train = Length of bridge + it's own length
=> (200+400)m
=> 600 m.
Speed = 36 kmph =(36×1000)/(60×60)= 10m/s
Hence, time taken = 600/10 s = 60s = 1min
Like if satisfied