Question

Worked out solution please

6. The door knob A is located at the point (0.2,1.2,0.9) meters in the coordinate system Oxyz. A force F = {-50, 0, 0.5) N is applied at A to shut the door. Find the moment of this force about the axis of the hinges. 2 Figure 6

Answer 1

Moment of the force F^rightarrow about the of hinge is given by, Vertical-bar M^rightarrow Vertical-bar = u^(r^rightarrow times F^rightarrow) u^, unit rector representing the axis Here u^= (o i^+ 1 j^+ ok^) r^rightarrow = (0.2 i^+ 1.2 j^+ 0.9 k^) m F^rightarrow = (-5 i^+ 0 j^+ 0.5 k^) N M = u^(r^rightarrow times F^rightarrow) = j^[(0.2 i^+ 1.2 j^+ 0.9 k^) times (-5 i^+ o j^+ 0.5 k^)] N - m = r^[- 0.1 i^+ 6 k^+ 0.6 i^- 4.5 j^] N - m = j^[0.6 i^- 4.6 j^+ 60 k^] N - m m = -4.6 N - m (moment of force about)