Write an expression for the two objects, moving with uniform velocities along the same striaght tracks but opposite in direction.

Explanation

(i) Consider two objects A and B moving with uniform velocities `V_(A) and V_(B)` along the same straight tracks but opposite in direction.
`vecv_(A)vecv_(B)`
(ii) The relative velocity of object A with respect to object B is
`vecV_(AB)=vecV_(A)-(-vecV_(B))=vecV_(A)+vecV_(B)`
(iii) The relative velocity of object B with respect to object A is
`vecV_(BA)=-vecB_(B)-vecV_(A)=-(vecV_(A)+vecV_(B))`
(iv) Thus, if two objects are moving in opposite directions, the magnitude of relative velocity of one object with respect to other is equal to the sum of magnitude of their velocities.