A small automated rover starts from rest and accelerates at a constant rate \(a\) along a straight horizontal testing track of length \(L\). At the end of the track, the rover reaches a final speed \(v_1\). The rover is then moved to a different track of length \(4L\) and again starts from rest, accelerating at the same constant rate \(a\). What is the speed of the rover at the end of the second track, \(v_2\), in terms of \(v_1\)?