3 Time taken by a train of length 1 metres to pass a pole or a standing man or a
signal post is equal to the time taken by the train to cover 1 metres.

4. Time taken by a train of length 1 metres to pass a stationary object of length b
metres is the time taken by the train to cover (1 + b) metres.

5. Suppose two trains or two bodies are moving in the same direction at u m / s and
v m/s, where u > v, then their relatives 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 is = (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 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)/(u-v) sec.

9. 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 speet) : (B's speed) = (b^{1/2}: a^{1/2}).