Solved Example & Practice Problems: Moment of Force about a Point in Space

Solved Examples for Understanding

Example 3.11.1 

A force acts at a point P(4, 3, 2) m. Determine the moment of this force about the point Q(2, 3, 4) m in vector form. Also find the magnitude of the moment and its angles with respect to x, y, z axes.

Solution : 

Example 3.11.2 

Determine the moment of the force F shown in Fig. 3.11.2 about the origin.

Solution: 

The required co-ordinates are A (− 3, 6, – 2), B (5, 9, – 3)

Example 3.11.3 

For the previous example, find moment of the force F about point P.

Solution :

Example 3.11.4 

A force acts at point A (1,2,3). Find a) Moment of the force about origin b) Moment of force about B (2, 1, 2) c) Component of this force along line AB.

Solution: 

Example 3.11.5 

Two forces F1 = 500 N and F2 = 600 N act along AB and AC as shown in Fig. 3.11.3. Determine the moment of the resultant of F1 and F2 about O.

Solution: 

The required co-ordinates are A (0, 10, 0), B (−, 1, 0, 5), C (6, 0, 2).

Example 3.11.6 

A rectangular plate is supported by brackets to the wall at A and B and host wire CD as shown in Fig. 3.11.4. Knowing that tension in wire is 200 N determine the moment about point A, of the force exerted by wire on point 'C'.

Solution: 

Examples for Practice

Q.1 

A force of magnitude 100 N acts from A(6, – 3, 7) m to B (- 4, 3, 2) m. Determine the moment of this force about the origin.

Q.2

A force of magnitude 200 N acts at point A(500, 0, 700) mm along the negative Z-direction. Determine the moment of force about the point B (0, 550, 300) mm.