Electric potential energy and work

[prophyasker]

Homework Statement

Positive point charge (Q = 8 μC, mass m = 19 g) is fixed at point (9 cm,0). A second identical charge q is constrained to slide on a frictionless wire along the y-axis. Assume: the only force on q is the electrostatic force. If q starts at (0,7 cm) and is released from rest, find its speed when it reaches (0,50 cm), in m/s.

Homework Equations

△V=W/Q
W=F*S=Q*E*S

The Attempt at a Solution

I attempt to use W=F*S=Q*E*S=1/2*m*vf^2 - 1/2*m*vi^2, but I got wrong.
thank you for your help

 

[Orodruin]

I attempt to use W=F*S=Q*E*S=1/2*m*vf^2 - 1/2*m*vi^2, but I got wrong.
thank you for your help

You need to provide your actual attempt, this is only a description of what you did and does not contain your actual computations.