an ion of mass 1.8 * 〖10〗^(-25) kg carrying a charge 4*〖10〗^(-16)c after being accelerated through a potential difference of 400V enters a uniform magnetic field of intensity 2*〖10〗^(-2) T
perpendicular to its direction of motion . calculate the radius of path described by the ion.
please give proper explanation about the formula that you will use.