Question

A train , 100 m long, is running at a speed of 54 km/hr. If it crosses a bridge in 12 seconds, find the length of the bridge.

Answer 1

If the bridge's length is x, then the train's engine has to move (x+100) meters to pull the last car across. So, since distance = speed * time,
x+100 = 54000 * 12/3600

Answer 2

change km/hr to m/s

find how long for the train to pass a given point ... t

length of bridge = (12 - t) * speed of train