The relation between time t and distance x is t=αx2+βx where α and β are constants. The retardation is
2αv3
2βv3
2αβv3
2β2v3
t=αx2+βx Differentiating: 1=2αdxdt⋅x+βdxdt v=dxdt=1β+2αx;dvdt=−2αv(β+2αx)2=−2αv3