Show that \(\mu = \frac { 2 } { 3 }\).
A small object of weight \(a W \mathrm {~N}\) is placed on the ladder at its mid-point and the object \(S\) of weight \(2 W \mathrm {~N}\) is placed on the ladder at its lowest point \(A\).
Given that the system is in equilibrium, find the set of possible values of \(a\).