The horizontal motion of the rock is a rectilinear motion. Then it is described as:
[tex]v=\frac{d}{t}[/tex]
If we want the distance to be 2x in the same time then the velocity will have to be:
[tex]\begin{gathered} v_x=\frac{2x}{t} \\ \frac{v_x}{2}=\frac{x}{t}_{} \end{gathered}[/tex]
Therefore the velocity will have to be:
[tex]\frac{v_x}{2}[/tex]
and the answer is a.
