Couldn't you merely relative the kinetic energy to its velocity, and hence the velocity to its radius? When you know the radius of the path taken, then you can determine where its position is when its travels half the circumfrence of a circle.
This is the question I am having difficult with. I really have no idea where to start.
Here's what I have gathered with the information provided:
Using the right hand rule, I've concluded v points along the x axis, the the force acting on the particle point along the z axis. Since the electron is under the influence of the magnetic field, and its radial acceleration is opposite in direction to the force, it will follow the path of a circle in the negative z direction. From here, I don't know where to go..
Thanks in advance.