Question

If a body is in equilibrium, we may conclude that

(A) No force is acting on the body.
(B) The resultant of all the horizontal forces acting on it is zero.
(C) The resultant of all the vertical forces acting on it is zero.
(D) The moments of the forces about any point is zero.

Choose the correct answer from the options given below.

• A. (A), (B) and (C) only.
• B. (B), (C) and (D) only.
• C. (A), (C) and (D) only.
• D. (A), (B) and (D) only.

Hint:

Equilibrium does not mean zero forces, it means the forces and their moments balance out.

Answer 1

The Correct Option is B

Step 1: Equilibrium of a rigid body means the body has no net tendency to move or rotate, it does not mean that no forces are acting on it at all. Several forces can act on a body and still cancel out perfectly, so statement (A) is not a valid conclusion, it is simply false in general.

Step 2: For a body in plane equilibrium, the standard conditions are that the sum of forces in the horizontal direction is zero, the sum of forces in the vertical direction is zero, and the sum of moments of all forces about any point is zero. These three conditions together (\(\Sigma F_x = 0\), \(\Sigma F_y = 0\), \(\Sigma M = 0\)) are exactly what define static equilibrium.

Step 3: So statement (B) is correct, statement (C) is correct, and statement (D) is correct.

Step 4: Since (A) is false and (B), (C), (D) are all true, the correct combination is (B), (C) and (D) only, which is option 2.