Question

question 5 of 5 policies current attempt in progress which one of the following statements describes the condition(s) for which a rigid body is in equilibrium? each external torque acting on the body must be zero. only internal forces can be present. the sum of the externally applied forces must be zero, and the sum of the externally applied torques must be zero. each external torque may not be non - zero, but the sum of the torques must be zero. each external force may be non - zero, but the sum of the forces must be zero.

Explanation:

For a rigid body to be in equilibrium, two conditions must be met. First, the sum of all externally applied forces acting on the body must be zero (\(\sum \vec{F} = 0\)), which ensures translational equilibrium (no linear acceleration). Second, the sum of all externally applied torques about any axis must be zero (\(\sum \vec{\tau}=0\)), which ensures rotational equilibrium (no angular acceleration).

• The first option “Each external torque acting on the body must be zero” is incorrect. It is the sum of torques that matters, not each individual torque.
• The second option “Only internal forces can be present” is wrong. External forces can be present as long as their sum (and sum of torques) is zero.
• The fourth option “Each external torque may not be non - zero, but the sum of the torques must be zero” is missing the force equilibrium condition.
• The fifth option “Each external force may be non - zero, but the sum of the forces must be zero” is missing the torque equilibrium condition.

Answer:

The sum of the externally applied forces must be zero, and the sum of the externally applied torques must be zero.