A body $A$ of mass $2\,\text{kg}$ is projected upward from the surface of the ground at $t = 0$ with a velocity of $20\,\text{m/s}$. One second later a body $B$, also of mass $2\,\text{kg}$, is dropped from a height of $20\,\text{m}$. If they collide elastically, then the velocities just after collision are: