Problems on Trains Important Formulas

• km/hr to m/s conversion:

    a km/hr =  a x 5         m/s.
    18

•     m/s to km/hr conversion:

    a m/s = a x  18         km/hr.
    5

•     Formulas for finding Speed, Time and Distance

•     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.

•     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.

•     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.

•     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.

•     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)

•     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)

•     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)