Answer
If the object's initial speed and final speed are the same, then the work done by the external forces is zero.
If the object's initial speed and final speed are not the same, then the work done by the external forces is non-zero.
Work Step by Step
If the object's speed is the same before starting and circle and after completing the circle, then the object's mechanical energy did not change. In that case, the work done by the external forces is zero.
However, if the object's speed changes, then the object's mechanical energy changes, which means that the work done by the external forces is non-zero.
