Drag is linear with velocity under Stokes' Law which assumes laminar flow and a very very low Reynolds number, and does not apply to ballistic projectiles flyin

Drag is linear with velocity under Stokes' Law which assumes laminar flow and a very very low Reynolds number, and does not apply to ballistic projectiles flying through air. Aerodynamic drag on the kinds of things that are involved in trebuchets is always quadratic with velocity.