Question

A charged particle travels undeflected through perpendicular electric and magnetic fields whose magnitudes are 4000 N/C and 20 mT,respectively.
Find the speed of the particle if it is a proton.
v= m/s
Find the speed of the particle if it is an alpha particle. (An alpha particle is a helium nucleus-a positive ion with a double positive charge of +2e.)
v= m/s

Answer 1

If there is no deflection, qE = q v B
with E and B oriented perpendicular to each other and the particle velocity. q is the charge of the particle.

v = E/B

The speed will not depend upon the charge or mass.

I assume your 20 mT field is milliTesla, not megaTesla.