1. The problem statement, all variables and given/known data An oscillator with mass 0.5 kg, stiffness 100 N/m, and mechanical resistance 1.4 kg/s is driven by a sinusoidal force of amplitude 2 N. Plot the speed amplitude and the phase angle between the displacement and speed as a function of the driving frequency and find the frequencies for which the phase angle for which the angle is 45 deg. 2. Relevant equations 3. The attempt at a solution Using the general form of the solution: x(t) = A(w) sin(wt-Φ) where Φ=atan(2wp/(w_0^2-w^2)) A(w) = (F/m)/((w_0^2-w^2)^2 + (2wp)^2)^0.5 I am positive the above equations are correct and come from the differential equation for this case. Now, u(t) [speed] = d x(t)/dt. = w*A(w)*cos(wt-Φ) =w*A(w)*sin(wt-Φ+pi/2) My question: Now the speed amplitude, I believe, is wA(w). Won't the phase angle between the displacement and velocity always be pi/2 irrespective of w?