physics
posted by :) on .
Figure 643 shows a "conical pendulum", in which the bob (the small object at the lower end of the cord) moves in a horizontal circle at constant speed. (The cord sweeps out a cone as the bob rotates.) The bob has a mass of 0.060 kg, the string has length L = 0.90 m and negligible mass, and the bob follows a circular path of circumference 0.90 m.
What is the period of the motion? The tension in the string is 0.596N.

The halfangle at the apex of the cone is theta = sin^1[0.9/2 pi)/0.9]
= sin^1(1/2 pi)
= 9.1 degrees
See http://en.wikipedia.org/wiki/Conical_pendulum
for the period of a conical pendulum. At this rather small cone angle, the period will be nearly the same as that of a normal pendualum of the same length. 
4sin^2(theta)  2sin(theta)  2 = 0 on the interval 0 (less than or equal to ) theta < 2(pi)?