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# Aptitude - Trains

## Important Terms

Speed in km/hr

a km /hr = (a * 5 / 18) m/s.

Speed in m/s

a m/s = ( a * 18/5) km/hr.

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 =

(a+b) / ( u+ v) sec.

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 =

( a+b) / (u + v ) sec.

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) = ( √b : √a ).