alleryStart learning →What is the first condition necessary for a system to be in equilibrium?
AThe total kinetic energy of the system is zero
BThe net external force on the system is zero
CThe net external torque about the cg is zero
DThe center of gravity sits above the pivot
Answer & Solution
Correct answer: B. The net external force on the system is zero
1. Newton's second law says net F = ma, so zero acceleration requires zero net external force.
2. That gives the first condition, net F = 0, which also forces net Fx = 0 and net Fy = 0.
3. A body in equilibrium may still be moving, so its kinetic energy need not be zero.
4. Zero net torque is the second condition, a separate requirement, not the first one.
_Source: OpenStax College Physics (CC BY 4.0), Ch 9 "Statics and Torque", section 9.1 The First Condition for Equilibrium_
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