Two blocks of masses $0.2\,\text{kg}$ and $0.5\,\text{kg}$ are placed a distance $d$ apart on a rough horizontal surface ($\mu = 0.5$). Each block is acted upon by a force of magnitude $3\,\text{N}$ directed toward the other block, as shown. They collide at $t = 2\,\text{s}$. Find $d$.