18. A mechanical or electrical system is described by the differential equation y + ω2y = f(t). Find y if f(t)= 1,0 a separately, remembering that f(t) = 0 for t > a. Show that 8>< 1 (1−cosωt), t: 1 [cosω(t−a)−cosωt], t>a. ω2 Sketch the motion if a = 1 T where T is the period for free vibrations of the system;