Question

6. Four forces act on an object such that the object is at rest. Three of the forces are given by

F1 = 2i −2j, F2 = i −4j, F4 = −3i −5j. Determine F3 and its magnitude

Answer 1

Let $F_3=ai+bj.$ Given the object is at rest

$$F_1+F_2+F_3+F_4=0$$

$$x-axis: 2+1+a-3=0=>a=0$$

$$y-axis: -2-4+b-5=0=>b=11$$

$$F_3=11j.$$

$$|F_3|=11$$