Question

a train 100m long is moving with a speed of 60km/h in what time shall it cross the bridge 1km long

Answer 1

length of train = 100 m 
speed of train = 60 km/hr or 50/3 m/sec
length of bridge = 1 km or 1000m
total length to be covered = 1000 + 100 = 1100 m 
speed = 50 / 3 m/sec
time taken = 1100 / 50 / 3
                  = 1100 *3 / 50 = 66 seconds

Answer 2

Total distance required for the train to cross the bridge is,

d = (100 + 1000) m = 1100 m

The speed of the train is,

v = 60 km/h = 60 × 5 / 18 = (50/3) m/s

Hence the time taken to cross the bridge is,

t = 1100 / (50/3) = 66 s.