Conservation of energy/momentum

1. The problem statement, all variables and given/known data
A proton with mass 1.59*10-27 kg is propelled at an initial speed of 3.49*105 m/s directly toward a uranium nucleus 4.97 m away. The proton is repelled by the uranium nucleus with a force of magnitude F = a/x2 where x is the separation between the two objects and a = 2.18 *10-26 Nm2. Assume that the uranium nucleus remains at rest. What is the speed of the proton when it is 8.60 *10-10 m from the nucleus?


2. Relevant equations

net force(F)=rate of change of momentum(dP/dt)
Total Energy before=Total Energy after
mathematically, E=kinetic energy(KE) before+potential energy(U) before=KE after + U after

3. The attempt at a solution
plugging in given values into the equations i think are relevant, but none of them get you any where..IS THERE AN EQUATION IM SUPPOSED TO USE?

 

P.S initial speed=3.49*10^5 and so on