Problem

When a charged particle moves perpendicular to a magnetic field, it experiences a force that depends on three things: how much charge it carries, how fast it's moving, and how strong the field is. The key insight is that the magnetic force formula $F = qvB\sin\theta$ simplifies beautifully when the motion is perpendicular to the field ($\theta = 90°$), so $\sin\theta = 1$. Just plug in the charge of the helium ion (which has lost both electrons), the given velocity and field strength, and you're done.

When a charged particle moves perpendicular to a magnetic field, it experiences a force that depends on three things: how much charge it carries, how fast it's moving, and how strong the field is. The key insight is that the magnetic force formula $F = qvB\sin\theta$ simplifies beautifully when the motion is perpendicular to the field ($\theta = 90°$), so $\sin\theta = 1$. Just plug in the charge of the helium ion (which has lost both electrons), the given velocity and field strength, and you're done.