1. A particle with charge $q$ and momentum $p$ is moving in the horizontal
plane under the action of a uniform vertical magnetic field of magnitude $B$.
Measurements are made of the particle's trajectory to determine the
\"sagitta\" $s$ and half-chord length $l$, as shown in the figure. Determine the
particle's momentum in terms of $q$, $B$, $s$, and $l$? (Assume $s << l$)