Note that the unit of magnetic flux density (B) is the Tesla, which is dimensionally equivalent to a
The velocity v of the proton may be found from the definition of potential difference, together with the principle of conservation of energy. Since by definition, potential difference between 2 points is defined as the work done per unit charge to move a positive charge between the 2 points, and this work done is transferred into kinetic energy of the proton, it implies that
This is a vector cross product so its direction can be obtained from the right hand rule, and is perpendicular to both v and B.
This force is hence directed towards the centre all the time and is thus the required centripetal force
The magnitude of this force can be given by
So, in this case,