Here is the problem: A singly charged positive ion has a mass of 2.50 X 10 ^-26 kg. After being accelerated through a potential difference of 250 V, the ion enters a magnetic field of 0.500 T, in a direction perpendicular to the field. Calculate the radius of the path of the ion in the field. I believe the formula to use is this: r = mv/qB and it should look like this with what is given: r = (2.5 X 10^-26 kg) v / (1.6 X 10^-19)(.50T) if that is correct, the only thing I'm having trouble with is the velocity. How do I find the velocity? if that isn't correct, then I'm lost. Thank you for your help.