Calculating Centripetal Force for Particle in Circular Motion

[buttontugger]

A particle of charge Q is fixed at the origin of an xy coordinate system. At t = 0 a particle (m = 0.694 g, q = 5.04 µC is located on the x-axis at x = 20.2 cm, moving with a speed of 34.0 m/s in the positive y direction. For what value of Q (in μC) will the moving particle execute circular motion? (Neglect the gravitational force on the particle.)

I tried plugging everything in, I just can't seem to figure out where to put the mass or velocity, if at all needed.

does F=k(.00504C)(Q)/(.202^2) ?

I really need somewhere to start

 

[Doc Al]

What must the acceleration be, if it's to execute circular motion? Apply Newton's 2nd law.

Note that µC means micro C = 10^-6 C.