Problem 1.11

Two particles move in a uniform gravitational field with an acceleration $g$. At the initial moment the particles were located at one point and moved with velocities $v_{1}=3.0 \mathrm{~m} / \mathrm{s}$ and $v_{2}=4.0 \mathrm{~m} / \mathrm{s}$ horizontally in opposite directions. Find the distance between the particles at the moment when their velocity vectors become mutually perpendicular.