Question

We know that relative velocity is Va-Vb.But sometimes relative velocity is Va-(-Vb)=Va+Vb why is that so?and sometimes Va is negative.why is that so?

Answer 1

Va - Vb  when  both are traveling in the same direction.

Va + Vb  when both are travelling towards each other.

Va  may be taken negative  if it is traveling in the opposite direction away from b and  b is traveling in the positive direction.