# Aptitude - Trains

## Important Terms

1. Speed in km/hr

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

2. Speed in m/s

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

3. 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.`

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 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.`

6. 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.`

7. 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.`

8. 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.`

9. 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 ).`

## Solved Examples

Solved Examples
aptitude_trains.htm 