Question

A body is in equilibrium under the influence of a number of forces. Each force has a different line of action. The minimum number of forces required is :

• A. 2, if their lines of action pass through the centre of mass of the body
• B. 3, if their lines of action are not parallel.
• C. 3, if their lines of action are parallel.
• D. 4, if their lines of action are parallel and all the forces have the same magnitude.

Answer 1

Answer: (B), (C), (D)

The correct options are
B 3, if their lines of action are not parallel.
C 3, if their lines of action are parallel.
D 4, if their lines of action are parallel and all the forces have the same magnitude.

If 2 lines of action pass through the centre of mass of the body and the forces have different magnitude so the resultant not zero.
If 3 lines of action are not parallel, the body is in equilibrium. One line of action must be the result of other two lines of action. similarly if 3 lines of action are parallel.
If 4 lines of action are parallel and all the forces have the same magnitude, the body is in equilibrium. The resultant must be zero.