Given :
Potential ,

Uniform magnetic field , B = 0.02 T .
Mass of proton ,
.
Charge on proton ,
.
Also , velocity of proton is perpendicular to magnetic field .
To Find :
The radius of the proton's resulting orbit .
Solution :
Now , when velocity is perpendicular to magnetic field radius of orbit is given by :
Putting all given values above :

Therefore , radius of orbit is 183.33 m .
Hence , this is the required solution .