Solution to task 448 from Chertov´s for extramural stud

Solution to task 448 from Chertov´s for extramural stud

448. The proton passed a certain accelerating potential difference U and flew into uniform fields crossed at right angles: magnetic (B = 5 mT) and electric (E = 20 kV / m). Determine the potential difference U, if a proton moves in a straight line in crossed fields.