  In this paper we review the system made up by two blocks connected by a
string over a smooth pulley with variable tension. One block lies on an
horizontal surface and the another block is hanging vertically. We carry out a
complete and systematic analysis for the tension of the string as function of
the angle and the horizontal distance x, at static equilibrium. We find a
simmetry-like that corresponds to two different confifigurations with the same
tension and obtain the relationship that must satisfy two angles or two
horizontal distances to obtain equal tension.
