Q.A particle having mass $m$ and charge $q$ is accelerated through a potential difference $V$. Find the force experienced when it is kept under a perpendicular magnetic field $\vec B$. [the four answer options in the source scan show fraction/exponent layout that flattened during OCR (digits and exponents run together outside their proper super/subscript positions) and could not be verbatim-transcribed with confidence -- held rather than guessed]