Uniform magnetic field problem

[mwadhwa]

Homework Statement

A proton, with mass 1.67*10^-27 kg and charge +1.6*10^-19C, is sent with velocity 5.0*10^4 m/s in the x-direction into a region where there is uniform electric field of magnitude 390 V/m in the y direction. What is the magnitude and direction of the uniform magnetic field in the region, if the proton is to pass through undeflected? Assume that the magnetic field has no x-component. Neglect gravitational effects.

Homework Equations

The Attempt at a Solution

I have no idea where to begin! Any help would be greatly appreciated!

 

[L-x]

can you at least think about which equations you might need in order to answer a question on a moving charge being deflected by an EM field?

You should then imagine a magnetic field does exist, of strength M, in some direction. Think about how the particle will move in this case and it should be obvious how to proceed.