Question

A 50 m long train passes over a bridge at a speed of 30km/hr. If it takes 36s to cross the bridge, calculate the length of the bridge.

Answer 1

Speed of train= 30 km/h= 30*1000 m/3600 s= 8.333333333333333333333333 m/s 
it takes 36 secs to cross the bridge means it travels it's own length+the length of the bridge. 
now velocity is given as 8.334 m/s that means 
in one sec the train travels 8.33333333333333333333333333 m 
so in 36 sec the train will travel 36*8.3333333333333333333333 m=300m 
That means 300 m = length of train+ length of bridge 
so length of bridge= 300- length of train 
Length of Bridge=300-50=250 m