How Does a Hard Disc Drive's Magnetic Field Affect an Electron's Motion?

[Zimtstange]

Homework Statement

I don't quite understand the following question, i get a very unrealistic result...

The write head of a hard disc drive produces a magnetic field of 95mT. The disc has a radius of 3.5 inches and rotates at 7200 rpm (rotations per minute). Calculate the Lorentz force acting on an electron near the edge of the disc.
Compare the result to the electron's weight.

Homework Equations

f = v/(2*$$\prod$$*r)

F= (m*v^2)/r

The Attempt at a Solution

i tried to solve it with this two equations but i got 4.6 * 10^-34 Newton for the Lorentzforce...

can somebody help me?

 

[Doc Al]

What's the formula for Lorentz force? (The force a magnetic field exerts on a moving charge.)