Question

draw position time graph for two objects moving along a straight line when their relative velocity is zero and positive?

Answer 1

zero relative velocity means the two objects are either stationary (both), or they are separated by the same displacement all the time.  That also means that they both have the same speed, velocity and acceleration.  They move in the same direction.

So the acceleration - time graph will be exactly same for both.  The velocity - time graph will be identical too.

The displacement (or position) - time graph will show two parallel curves, separated by a vertical difference (b-a) as in :

          s1 = a + u t + 1/2 a t^2
          s2 = b + u t + 1/2 a t^2