Halliday, Resnick & Walker — Oscillations: Problem 39

39 The angle of the pendulum of Fig. 15-11b is given by \(\theta = \theta_m \cos[(5.63 \text{ rad/s})t + \phi]\). If at \(t = 0\), \(\theta = 0.040 \text{ rad}\) and \(d\theta/dt = -0.200 \text{ rad/s}\), what are (a) the phase constant \(\phi\) and (b) the maximum angle \(\theta_m\)? (Hint: Don’t confuse the rate \(d\theta/dt\) at which \(\theta\) changes with the \(\omega\) of the SHM.)