Velocity selector problem-physics hurts!

Question

i know i seem desperate with like 5 posts, but i have been stuck on these for some time..can someone help!?

A proton accelerates from rest through a potential of 16.0 kV. It then enters a velocity selector, consisting of a parallel plate capacitor and a magnetic field.

Between the capacitor plates the electric field is 3.10×105 N/C. What is the magnetic field such that the proton passes through the region without deflection?

Answer 1

set the magnetic force and the electric force equal to each other and plug in all known variables, leaving only the magnetic field strength B to be solved for.

Answer 2

I love the velocity selector problems.

The velocity of the proton after accelerating though the potential difference is:

v = (2e∆V / m)^(1/2)

= ((2 x (1.60 x 10^-19 C) x 16,000 V) / (1.67 x 10^-27 kg))^(1/2)

= 1.75 x 10^6 m/s

For there to be zero deflection, the magnetic field must be:

B = E / v

= (3.10 x 10^5 N/C) / (1.75 x 10^6 m/s)

= 0.177 T

If you need to know the direction of the field, use the right hand rule.