Finding velocity of particles in a uniform magnetic field

[ILstudent122]

Homework Statement

Given are a uniform electric field, E = 30,000 V/m inside a capacitor (see picture), and a uniform magnetic filed, B = 10 T, perpendicular to the plane of the page, present in all of the area.

Identical charged particles are moving in a trajectory marked by the dashed line, under the influence of the two fields: The trajectory inside the capacitor is a straight line, and the trajectory outside the capacitor is circular, with radius r = 1 cm.

What is the velocity v of the charged particles?

Homework Equations

Possibly r = mv / qB , but I don't know the mass of the particle.
Maybe E = F/q

The Attempt at a Solution

I know that the magnetic field is into the page based on the RHR. The particle is in circular motion because of the velocity and magnetic force vectors. The answer is v = 3000 m/s but I have no idea how it was derived.

 

[TSny]

How many forces act on the particles while they are between the plates of the capacitor?

What can you say about these forces given the fact that the particles are traveling in a straight line with a constant speed between the plates?

 

[TSny]

Just noticed that this is your first post at PhysicsForums, ILstudent122. Welcome!