Question

Determine graphically the magnitude and direction of the resultant of these three coplanar forces, which may be considered as acting at a point: Force A, 12 N acting horizontally to the right; force B, 7 N inclined at 60° to force A; force C, 15 N inclined at 150° to force A.

Answer 1

The space diagram is shown in Figure 3.14. The vector diagram shown in Figure 3.15, is produced as follows:

(i) oa represents the 12 N force in magnitude and direction

(ii) From the nose of oa, ab is drawn inclined at 60° to oa and 7 units long

(iii) From the nose of ab, bc is drawn 15 units long inclined at 150° to oa (i.e. 150° to the horizontal)

(iv) oc represents the resultant; by measurement, the resultant is 13.8 N inclined at φ = 80° to the horizontal.

Thus the resultant of the three forces, FA, FB and FC is a force of 13.8 N at 80° to the horizontal.