Frequently, attention in an equilibrium situation is confined to a plane. An example would be a ladder leaning against a wall, which is in danger of slipping only in the plane perpendicular to the ground and wall. By orienting a Cartesian coordinate system so that the x and y axes are in this plane, choose which of the following sets of quantities must be zero to maintain static equilibrium in this plane.
\sum F_x and \sum \tau_z and \sum F_y
\sum F_z and \sum \tau_x and \sum \tau_y
\sum \tau_x and \sum F_x and \sum \tau_y and \sum F_y
\sum \tau_x and \sum F_x and \sum \tau_y and \sum F_y and \sum \tau_z