Medical cyclotrons need efficient sources of protons to inject into their center. In one kind of ion source, hydrogen atoms (i. e., protons with one orbiting electron) are fed into a chamber where there is a strong magnetic field. Electrons in this chamber are trapped in tight orbits, which greatly increases the chance that they will collide with a hydrogen atom and ionize it. One such source uses a magnetic field of 90 mTmT, and the electrons' kinetic energy is 1.4 eV. Required:
If the electrons travel in a plane perpendicular to the field, what is the radius of their orbits?

The radius is

Explanation:

From the question we are told that

    The magnetic field is  

     The electron kinetic energy is  

Generally for the collision to occur the centripetal force of the electron in it orbit is equal to the magnetic force applied  

   This is mathematically represented as

=>    

Where  m is the mass of electron with values  

             v is the escape velocity  which is mathematically represented as

So  

     apply indices

substituting values

the answer is to check all of them! they all apply well at least i think so!

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me