TRAINS:
Two trains of length $$L_1$$ and $$L_2$$ travelling at speeds of $$S_1$$ and $$S_2$$ cross each other, the trains have to travel a distance of $${L_1+L_2}$$
- Time for a train to cross a stationary object (pole/person) = L/S
- Time for a train to cross a platform = (L + platform length)/S
