A Geophysicist Measures the Magnetic Force on a Proton That $1.996 \mathrm {~km} / \mathrm { s }$

A geophysicist measures the magnetic force on a proton that is moving vertically downward at a point $1.996 \mathrm {~km} / \mathrm { s }$ at the earth's equator. At that Iocation, the earth's magnetic magnetic field is horizontal and has a strength of $0.40 \times 10 ^ { - 4 } \mathrm {~T}$ . What are the magnitude and direction of the force she will measure? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$