Physics 2008 JAMB Past Questions - Question 9: I All the three forces must be concurrent II. The upwards forces is equal to the downwards force III.The algebraic sum of the moment about any points must be zero .Which of the above conditions must hold for a body acted upon by a system of three coplanar forces in equilibrium ?

Correct Answer

D

Explanation

option ii is one of the conditions of an equilibrium of parallel forces only I and iii are correct

In order for a body acted upon by a system of three coplanar forces to be in equilibrium, all three of the given conditions must hold. Let's break down each of these conditions:

I. All the three forces must be concurrent:
This means that the three forces must meet or intersect at a single point. If the forces are not concurrent, the body will not be in equilibrium.

II. The upwards force is equal to the downwards force:
This condition ensures that the net vertical force acting on the body is zero. In other words, the sum of all the forces acting upwards must be equal to the sum of all the forces acting downwards.

III. The algebraic sum of the moment about any point must be zero:
This condition involves the concept of moments or torques. The moment of a force about a point is the force multiplied by the perpendicular distance from the point to the line of action of the force. For the body to be in equilibrium, the sum of the moments (or torques) about any point must be zero. This condition ensures that the body is not rotating due to the applied forces.

So, to have a body in equilibrium under the influence of a system of three coplanar forces, all three conditions (I, II, and III) must be satisfied.