QUESTIONS AND PROBLEMS. CHAPTER III. 



53 



16. A force of 8000 Ibs. acts 6 inches from the center of a 

 wall; if it be taken as acting at the center of the wall, what will 

 be the moment of the couple which must be introduced? 



17. A force of 6000 Ibs. acts vertically downward and a 

 force of 10000 Ibs. vertically upward; their lines of action are 

 5 ft. apart; what is their resultant, and how far from the line of 

 action of the greater force is its line of action? Ans. 7 ft. 



18. What are the conditions for complete equilibrium of a 

 body acted upon by a system of forces algebraically and 

 graphically? 



19. What is the foundation of the force polygon? 



20. If the direction of two forces in the force polygon were 

 opposite to that of all the other forces, what would it indicate? 



21. What is the fundamental principle used in drawing a 

 resultant polygon? A string polygon? 



22. If in Fig. 24 RI, P 2 , and PI were known, what would 

 ACDB be? 



23. What is the function of the string polygon in Fig. 28? 

 In Fig. 32? In Fig. 43? In Figs. 63 and 64? 



24. How are the points A and chosen in Fig. 28? 



25. If the string polygon of Fig. 28 is considered as a 

 framed structure, to what will the stress in BC be equal? In GD? 



26. How may the closing line in Fig. 42 be made horizon- 

 tal? In Fig. 28? 



27. Where is the resultant of the loads in Fig. 43 located? 

 In Fig. 61? In Fig. 64? 



28. What is the difference between the string polygon and 

 the resultant polygon? 



29. If there is complete equilibrium when R = and M = 

 0, why are there three independent equations? 



30. Which of the eight directions given in Art. 40 plainly 

 lead to a saving of time? Which to reliable results? Which to 

 accuracy? 



31. By which of the six methods of application of the 

 equations of equilibrium are reactions obtained? By which 

 stresses? 



32. In Figs. 59 and 60, do the arrows on the members cut 

 by the section represent the forces exerted by the part shown 

 upon the other part, or vice versa? 



33. Show how a curved section would be more convenient 

 than a straight one in getting, stress PQ in Fig. 53. 



