An extended object is in static equilibrium if only the net torque acting on the object is zero. either the net force acting on the object is zero or the net torque acting on the object is zero. only the net force acting on the object is zero. both the net force acting on the object is zero and the net torque acting on the object is zero.

An extended object is in static equilibrium if both the net force acting on the object is zero and the net torque acting on the object is zero. This means that there is no unbalanced force or torque acting on the object that could cause it to start moving or rotating.

Here's a step-by-step explanation:

1. Net Force: The net force acting on an object is the vector sum of all the forces acting on it. If the net force is zero, it means that the object is either at rest or moving with a constant velocity. In the context of static equilibrium, the object is at rest.

2. Net Torque: The net torque acting on an object is the vector sum of all the torques acting on it. Torque is a measure of the force that can cause an object to rotate about an axis. If the net torque is zero, it means that the object is not experiencing any rotational acceleration.

3. Static Equilibrium: An object is in static equilibrium if it is at rest and remains at rest, i.e., it is not in motion and will not start moving or rotating on its own. For an object to be in static equilibrium, both the net force and the net torque acting on it must be zero.

So, the correct statement is: "An extended object is in static equilibrium if both the net force acting on the object is zero and the net torque acting on the object is zero."