Sans frottement : Z = somme -> -> ZF = ma -> -> ZF . y = mg = may => g=ay Uy(t) = Uy0 + Vy0 t + 1/2 gt^2 avec frottement b = alpha -> -> ZF . y = mg - b Vy = may . => mg - b Vy = m V(t) . => m V(t) + b Vy(t) = mg . => V(t) + b/m Vy(t) = g On pose k = b/m . => V(t) + k Vy(t) = g -> homogene . Vy(t)+k Vy(t) = 0 . Vy = -kVy . => Vy/Vy = -k => lr'(Vy)=-k on intègre => lr(Vy)=-kt+cst Vy = e(-kt+cst) = e(-kt)e(cst) = De(-kt) 2 Solution particulière 0+k Vy = g => Vy = g/k