A particle of mass 40 mg and carrying a charge `5 xx 10^(-9) C` is moving directly towards a fixed positive point charge on magnitude `10^(-8) C`. When it is at a distance of 10 cm from the fixed positive point charge it has a velocity of `50 cm s^(-1)` at what distance from the fixed point charge will the particle come momentarily to rest ? Is the acceleration constant during motion?