12.
The resultant of the following three couples 20 kg force, 0.5 m arm, +ve sense 30 kg force, 1 m arm, -ve sense 40 kg force, 0.25 m arm, +ve sense having arm of 0.5 m will be

13.
Center of percussion is

15.
The algebraic sum of the resolved parts of a number of forces in a given direction is equal to the resolved part of their resultant in the same direction. This is as per the principle of

16.
The magnitude of two forces, which when acting at right angle produce resultant force of $$\sqrt {10} $$  kg and when acting at 60° produce resultant of $$\sqrt {13} $$  kg. These forces are

18.
If three forces acting in one plane upon a rigid body, keep it in equilibrium, then they must either

19.
In determining stresses in frames by methods of sections, the frame is divided into two parts by an imaginary section drawn in such a way as not to cut more than