System of parallel forces:

A rigid body is subjected to system of parallel forces as shown in the figure. Reduce this system to,

(i) A single force system

(ii) A single force moment system at point B

Sol.: It is equivalent force system

(Acting downward)

R = 15 - 60 + 10 -25 = -60 N

Now taking moment about A, apply varignon's theorem

R.X = 60 × 0.4 - 10 × 0.7 + 25 × 1.4

60.X = 52, × = 0.867 m Where X is distance of resultant from point A.
(1) A single force be 60 N which is acting downward

(2) Now a force of 60 N = A force of 60 N (down) at point B

and anticlockwise moment of 60 × (1.4 - 0.866) = 31.98 Nm at B.

60 N force and 31.98 Nm moment anticlockwise                                                         .......ANS