A little calculus is needed for this problem.
v = x1/2 = dx/dt
The differential equation: x1/2 = dx/dt can be solved by the method of separation of variables.
dt = dx/ x1/2 Integrate both sides
t + c = 2 x1/2 so x(t) = [( t + c) / 2 ]2 c is a constant of integration
Since x(0) = 0 this implies that c = 0
Finally x(t) = ( t/2)2