Two stones are thrown vertically upwards simultaneously from the same point on the ground with initial speed ${\mathrm{u}}_1=30\mathrm{m}/\mathrm{s}$ and ${\mathrm{u}}_2=50\mathrm{m}/\mathrm{s}$. For the time interval in which both reach the ground, which of the curve represent correct variation of $\left({\mathrm{x}}_2-{\mathrm{x}}_1\right)=$ the relative position of second stone with respect to first with time (t)? 
$\left({\mathrm{v}}_2-{\mathrm{v}}_1\right)=$ the relative velocity of second stone with respect to first with time (t).
Assume that stones do not rebound after hitting.