A pendulum of length l and mass m is subjected to a damping force proportional to the velocity, given by b(dθ/dt), and a periodic driving torque given by τ(t)=τ0cos(ωt). The equation of motion for the angular displacement θ is ml2(d2θ/dt2)+b(dθ/dt)+mglθ=τ0cos(ωt).
Determine what the solution to this equation will be given that A=ml2(ω2−g/l)2+(b2ω2/m2l2)τ0 and ϕ=tan−1(ω(b/ml2)g/l−ω2).