Equilibrium in Physics

Steps:

• Define equilibrium: An object is in equilibrium if it has no linear or angular acceleration.
• For no linear acceleration, net force (resultant force) must be zero.
• For no angular acceleration, net torque (resultant torque) must be zero.
• Match options to this condition: Only zero net force and torque satisfy both.

Why A is correct:

• It directly states the conditions from Newton's first law extended to rotation: ∑F = 0 and ∑τ = 0 ensure static or constant motion equilibrium.

Why the others are wrong:

• B: Non-zero resultant force and torque cause acceleration, violating equilibrium.
• C: Zero torque alone prevents rotation but allows translation if force is non-zero.
• D: Balances vertical forces but ignores horizontal forces and torques.

Final answer: A