Problems on Trains - Important Formulas | Aptitude

1. km/hr to m/s conversion:

   a km/hr =		a x	5		m/s.
   			18

2. m/s to km/hr conversion:

   a m/s =		a x	18		km/hr.
   			5

3. Formulas for finding Speed, Time and Distance
4. Time taken by a train of length l metres to pass a pole or standing man or a signal post is equal to the time taken by the train to cover l metres.
5. Time taken by a train of length l metres to pass a stationery object of length b metres is the time taken by the train to cover (l + b) metres.
6. 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.
7. Suppose two trains or two objects bodies are moving in opposite directions at u m/s and v m/s, then their relative speed is = (u + v) m/s.
8. If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then:

   The time taken by the trains to cross each other =	(a + b)	sec.
   	(u + v)

9. If two trains 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)	sec.
   	(u - v)

10. 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)