Problem

When a charged particle moves in a magnetic field, the magnetic force provides centripetal acceleration, linking the radius of curvature to the particle's momentum and charge. Since all three particles have the same kinetic energy but different masses and charges, you need to express momentum in terms of that shared energy, then use $r = \frac{mv}{qB}$ to compare their radii. The key insight is that heavier particles and those with smaller charge will curve less sharply—so track how mass and charge compete in determining the trajectory size.

When a charged particle moves in a magnetic field, the magnetic force provides centripetal acceleration, linking the radius of curvature to the particle's momentum and charge. Since all three particles have the same kinetic energy but different masses and charges, you need to express momentum in terms of that shared energy, then use $r = \frac{mv}{qB}$ to compare their radii. The key insight is that heavier particles and those with smaller charge will curve less sharply—so track how mass and charge compete in determining the trajectory size.