  We examine some basic physics surrounding regenerative braking and air drag.
First, we analyze under what conditions it becomes energetically favorable to
use aggressive regenerative braking to reach a lower speed over ``coasting''
where one relies solely on air drag to slow down. We then proceed to
reformulate the question as an optimization problem to find the
velocity-profile that maximizes battery charge. Making a simplifying assumption
on battery-charging efficiency, we formulate the recovered energy as an
integral quantity and solve the associated Euler-Lagrange equation to find the
optimal braking curve. Using Lagrange-multipliers, we also explore the effect
of adding a fixed-displacement constraint.
