Trains problem are depends on the concept of time, distance and speed.
Speed in km/hr
Speed in m/s
Time taken by a train of length L metres to pass a pole or a standing man or a signal post is equal to the time taken by the train to cover
L Metres.
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.
Suppose two train or two bodies are moving in the same direction at u m/s and v m/s , where u > v, then their
relative speed = (u - v) m/s.
Suppose two trains or two bodies are moving in opposite directions at u m/s and v m/s , then their
relative speed = ( u + v) m/s.
If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then time taken by the trains to cross each other
If two train s of length a metres and b metres are moving in the same direction at u m/s and v m/s , then the time taken by the faster train to cross the slower train
If two train ( 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 speed) : ( B speed) = ( vb : va ).