A body is in equilibrium under three concurrent forces. If two forces are perpendicular, the third force must be: MCQ with Answer and Explanation

For equilibrium, net force = 0. If forces F₁ and F₂ are perpendicular, their vector sum R = √(F₁² + F₂²). The third force F₃ must balance R, so F₃ = -R, i.e., equal in magnitude and opposite in direction to the vector sum of F₁ and F₂. Memory aid: 'Equilibrium: vector sum of all forces = 0; third force closes the triangle'. This statics concept is frequently tested in competitive exams. Always use vector addition for force equilibrium; scalar sum is incorrect for non-collinear forces.