READING QUIZ. 2. When using the method of joints, typically equations of equilibrium are applied at every joint. A) Two B) Three C) Four D) Six

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1 READING QUIZ 1. One of the assumptions used when analyzing a simple truss is that the members are joined together by. A) Welding B) Bolting C) Riveting D) Smooth pins E) Super glue 2. When using the method of joints, typically equations of equilibrium are applied at every joint. A) Two B) Three C) Four D) Six

2 CONCEPT QUIZ 1. Truss ABC is changed by decreasing its height from H to 0.9 H. Width W and load P are kept the same. Which one of the following statements is true for the revised truss as compared to the original truss? B A P H C A) Force in all its members have decreased. W B) Force in all its members have increased. C) Force in all its members have remained the same. D) None of the above.

3 CONCEPT QUIZ (continued) F F F 2. For this truss, determine the number of zero-force members. A) 0 B) 1 C) 2 D) 3 E) 4

4 ATTENTION QUIZ 1. Using this FBD, you find that F BC = 500 N. Member BC must be in. F BC A) Tension B) Compression B F BD C) Cannot be determined B Y 2. For the same magnitude of force to be carried, truss members in compression are generally made as compared to members in tension. A) Thicker B) Thinner C) The same size

5 READING QUIZ 1. In the method of sections, generally a cut passes through no more than members in which the forces are unknown. A) 1 B) 2 C) 3 D) 4 2. If a simple truss member carries a tensile force of T along its length, then the internal force in the member is. A) Tensile with magnitude of T/2 B) Compressive with magnitude of T/2 C) Compressive with magnitude of T D) Tensile with magnitude of T

6 1. Can you determine the force in member ED by making the cut at section a-a? Explain your answer. A) No, there are 4 unknowns. B) Yes, using M D = 0. C) Yes, using M E = 0. D) Yes, using M B = 0. CONCEPT QUIZ

7 CONCEPT QUIZ 2. If you know F ED, how will you determine F EB? A) By taking section b-b and using M E = 0 B) By taking section b-b, and using F X = 0 and F Y = 0 C) By taking section a-a and using M B = 0 D) By taking section a-a and using M D = 0

8 ATTENTION QUIZ 1. As shown, a cut is made through members GH, BG and BC to determine the forces in them. Which section will you choose for analysis and why? A) Right, fewer calculations. B) Left, fewer calculations. C) Either right or left, same amount of work. D) None of the above, too many unknowns.

9 ATTENTION QUIZ 2. When determining the force in member HG in the previous question, which one equation of equilibrium is best to use? A) M H = 0 B) M G = 0 C) M B = 0 D) M C = 0

10 READING QUIZ 1. Frames and machines are different as compared to trusses since they have. A) Only two-force members B) Only multiforce members C) At least one multiforce member D) At least one two-force member 2. Forces common to any two contacting members act with on the other member. A) Equal magnitudes but opposite sense B) Equal magnitudes and the same sense C) Different magnitudes but opposite sense D) Different magnitudes but the same sense

11 CONCEPT QUIZ 1. The figures show a frame and its FBDs. If an additional couple moment is applied at C, then how will you change the FBD of member BC at B? A) No change, still just one force (F AB ) at B. B) Will have two forces, B X and B Y, at B. C) Will have two forces and a moment at B. D) Will add one moment at B.

12 CONCEPT QUIZ (continued) D 2. The figures show a frame and its FBDs. If an additional force is applied at D, then how will you change the FBD of member BC at B? A) No change, still just one force (F AB ) at B. B) Will have two forces, B X and B Y, at B. C) Will have two forces and a moment at B. D) Will add one moment at B.

13 1. When determining the reactions at joints A, B, and C, what is the minimum number of unknowns for solving this problem? A) 3 B) 4 C) 5 D) 6 ATTENTION QUIZ 2. For the above problem, imagine that you have drawn a FBD of member AB. What will be the easiest way to write an equation involving unknowns at B? A) M C = 0 B) M B = 0 C) M A = 0 D) F X = 0

14 READING QUIZ 1. A friction force always acts to the contact surface. A) Normal B) At 45 C) Parallel D) At the angle of static friction 2. If a block is stationary, then the friction force acting on it is. A) s N B) = s N C) s N D) = k N

15 CONCEPT QUIZ 1. A 100 lb box with a wide base is pulled by a force P and s = 0.4. Which force orientation requires the least force to begin sliding? A) P(A) B) P(B) 100 lb C) P(C) D) Can not be determined P(A) P(B) P(C) 2. A ladder is positioned as shown. Please indicate the direction of the friction force on the ladder at B. A) B) C) D) A B

16 ATTENTION QUIZ 1. A 10 lb block is in equilibrium. What is the magnitude of the friction force between this block and the surface? A) 0 lb B) 1 lb C) 2 lb D) 3 lb S = lb 2. The ladder AB is postioned as shown. What is the direction of the friction force on the ladder at B. B A) B) C) D) A

17 READING QUIZ 1. A wedge allows a force P to lift a weight W. A) (large, large) B) (small, small) C) (small, large) D) (large, small) W 2. Considering friction forces and the indicated motion of the belt, how are belt tensions T 1 and T 2 related? A) T 1 > T 2 B) T 1 = T 2 C) T 1 < T 2 D) T 1 = T 2 e

18 CONCEPT QUIZ 1. Determine the direction of the friction force on object B at the contact point between A and B. A) B) C) D) 2. The boy (hanging) in the picture weighs 100 lb and the woman weighs 150 lb. The coefficient of static friction between her shoes and the ground is 0.6. The boy will? A) Be lifted up B) Slide down C) Not be lifted up D) Not slide down

19 ATTENTION QUIZ 1. When determining the force P needed to lift the block of weight W, it is easier to draw a FBD of first. W A) The wedge B) The block C) The horizontal ground D) The vertical wall 2. In the analysis of frictional forces on a flat belt, T 2 = T 1 e. In this equation, equals. A) Angle of contact in degrees B) Angle of contact in radians C) Coefficient of static friction D) Coefficient of kinetic friction

20 READING QUIZ 1. A screw allows a moment M to lift a weight W. W A) (large, large) B) (small, small) C) (small, large) D) (large, small) 2. A screw is self locking if it remains in place under loads. A) any axial B) small axial C) any rotational D) small rotational

Announcements. Trusses Method of Joints

Announcements. Trusses Method of Joints Announcements Mountain Dew is an herbal supplement Today s Objectives Define a simple truss Trusses Method of Joints Determine the forces in members of a simple truss Identify zero-force members Class