일반물리학 1 — Oscillations: Problem 62

62 Suppose that a simple pendulum consists of a small 60.0 g bob at the end of a cord of negligible mass. If the angle \(\theta\) between the cord and the vertical is given by \(\theta = (0.0800 \text{ rad}) \cos[(6.80 \text{ rad/s})t + \phi]\), what are (a) the pendulum’s length and (b) its maximum kinetic energy?