Question 793214
As both balls are falling, at all times the first ball's speed is greater than the speed of the second ball, so the distance between them increases.
 
In formulas, the distance is
{{{gt^2/2-g(t-1)^2/2=g(t^2-(t^2-2t+1))/2=g(t^2-t^2+2t-1)/2=g(2t-1)/2}}}
which increases linearly with {{{t}}}.