A rigid body in mechanical equilibrium is undergoing neither linear nor rotational acceleration; however it could be translating or rotating at a constant velocity.---could not quite understand this.. can u please xplain?

The necessary conditions for mechanical equilibrium for a system of particles are:

(i)The vector sum of all external forces is zero;

(ii) The sum of the moments of all external forces about any line is zero.

As applied to a rigid body, the necessary and sufficient conditions become:

A rigid body is in mechanical equilibrium when the sum of all forces on all particles of the system is zero, and also the sum of all torques on all particles of the system is zero.

A rigid body in mechanical equilibrium is undergoing neither linear nor rotational acceleration; however it could be translating or rotating at a constant velocity.

Therefore for linear or rotational acceleration we required a net force whereas for translating or rotating at a constant velocity,we don't required a net force.