Question

What is the relative velocity when two bodies move in opposite direction?

Answer 1

When two bodies A and B move in opposite direction,

Velocity of A relative to B is given by
${\overrightarrow{V}}_{AB}={\overrightarrow{V}}_A-{\overrightarrow{V}}_B$
If we consider positive x-axis along ${\overrightarrow{V}}_A$,
${\overrightarrow{V}}_A=V_A\hat{i}$ and ${\overrightarrow{V}}_B=-V_B\hat{i}$ (since B moves in opposite direction)
${\overrightarrow{V}}_{AB}=V_A\hat{i}-(-V_B\hat{i})$
${\overrightarrow{V}}_{AB}=(V_A+V_B)\hat{i}$
So, relative velocity is given by $(V_A+V_B)$