[填空题]
A clock pendulum oscillates at a frequency ofbhd:hd 40)imt9v f,adl 3mh d; 2.5 ld;u8s.i wx)srfe..qe 0 e ak0Hz. At it is released from rest starting at an angle 8 wesa r.x. ui0).kde;0lqf seof 15 $^{\circ} $ to the vertical. Ignoring friction, what will be the position (angle) of the pendulum at
(a) t = 0.25 s , $^{\circ} $
(b) t = 1.60 s , $^{\circ} $
(c) t = 500 s ? $^{\circ} $
[Hint: Do not confuse the angle of swing $\theta$ of the pendulum with the angle that appears as the argument of the cosine.]
