tow trains are moving i opposite directions @60km/hr n 90Km/hr .their lengths r 1.10km n 0.9 km respectively.the time taken by the slower train to cross the faster trai in seconds? this d q of relative velocity . i knw d as but i want to clarify one thing y r we adding the length of two trains? for solving this pblm.

Question

tow trains are moving i opposite directions @60km/hr n 90Km/hr .their lengths r 1.10km n 0.9 km respectively.the time taken by the slower train to cross the faster trai in seconds?  this d q of relative velocity . i knw d as but i want to clarify one thing y r we adding the length of two trains? for solving this pblm.

anonymous · Answer

suppose   that  you  are standing   in the  engine  of the  first train  , then the   instant of  crossing the  trains  start  when the  second train's  engine  just passes by  you  and     it will  last till  the  last boggie   of the train  passes the    last   boggie of  first   train. so  in talking  realtively , we  add  the  length of two trains