3). Time taken by a train of length l meters to pass a pole or a standing man or a signal
    post is equal to the time taken by the train to cover l meters.


    4). Time taken by a train of length l metres to pass a stationary object of length b metres
    is the time taken by the train to cover (l + b) metres. 


    5). Suppose two trains or two objects bodies are moving in the same direction at u m/s
    and v m/s, where u > v, then their relative speed is = (u - v) m/s.


   6). If two trains (or bodies) start at the same time from points A and B towards each other
   and after crossing they take a and b sec in reaching B and A respectively, then 
(A's speed) : (B's speed) = (√ b  : √ a)