The figure shows: a) a chain LR, b) a chain RC and c) a mechanical system - a body of mass m moves in a medium with viscous friction F = -gv. In examples a and b, voltage oscillations across the capacitor and across the resistance are excited by external emf f(t). In example c, an external force f(t) acts on the body. Show that the equation governing the behavior of all three systems is S + S = f(t), where m = L/R in example a, m = RC in example b, and m = m/g in example c.

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