The relation between time t and distance x is x is t=ax2+βx where α and β are constants The retardation is
2αv3
2βv3
2αβv3
2b2v3
t=αx2+βx Differentiating: 1=2αdxdtx+βdxdt∣ v=dxdt=1β+2αx;dvdt=−2αv(β+2αx)2=−2αv3