Question

8. Find the resultant moment of the forces F1 = 4N, F2 = 6N forming an angle 30⁰ with the rod and F3 = 2N acting on the rod having a rotational axis O at its end.

Answer 1

Rule #1: to find moment, we use forces (or their components) perpendicular to the rod, so, we will need to find the vertical component of 6N-force:

$$F_6=6·\sin30°=3\text{ N}.$$

Moments clockwise are negative, counter-slockwise are positive. The resultant moment is

$$m=-4·1-3·0.5+2·3=0.5\text{ N}·\text{m}.$$

Thus, the rod will rotate counter-clockwise.