A particle of mass 1.0mg carries a charge of +1.0nC. It is launched from the origin with a speed of 0.50m/s directly along the +x-axis. The electric potential along this axis is given by V(x)=4x2, where x is in meters and V in volts. Neglecting all forces other than the electric force, at what x-coordinate will the particle momentarily come to rest before reversing direction?
a) 11m
b) 5.6m
c) 7.9m
d) 4.0m