The height of pivot point above the plane of rotation is h
cosi=h/Li
cosf=h/Lf
Lf=Li•cosi/cosf
A small mass m swings in a horizontal circle of radius r at the end of a string of length Li and
negligible mass, which makes an angle �i with the vertical. The string is slowly shortened (for
example by pulling it through a hole in its support) until the final length is Lf and the string is
making an angle �f with the vertical. Find an expression for Lf in terms of Li; �i and �f .
1 answer