11.7 Exercise 11

The mass and charge of a water droplet are $1.0 \times 10^{−4} \text{g}$ and $2.0 \times 10^{−8} \text{C} ,$ respectively. If the droplet is given an initial horizontal velocity of $5.0 \times 10^{5} \hat{i} \text{m}/\text{s} ,$ what magnetic field will keep it moving in this direction? Why must gravity be considered here?