TALLER DE TORQUE. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

Transcripción

1 TALLER DE TORQUE MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) What condition or conditions is/are necessary for rotational equilibrium? 1) A) Fy = 0 B) Fx = 0, Fy = 0, = 0 C) Fx = 0 D) Fx = 0, Fy = 0 E) = 0 2) A pencil balanced on its tip such that it does not move 2) A) is in unstable equilibrium. B) is in stable equilibrium. C) has a net vertical force. D) has a zero moment of inertia. E) has a net torque acting on it. Figura ) En la Figura 11.4, cuanta masa M se requiere para equilibrar el móvil? 3) A) 60 gms B) 90 gms C) 30 gms D) 36 gms E) 18 gms SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 4) The mobile shown in the figure is perfectly balanced, and the horizontal supports have insignificant masses. What must be the masses of the suspended objects m1, m2, and m3 to maintain balance? 4)

2 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. Figura ) Una viga no uniforme de 200 kg, de 6.0 m de largo es fijada ligeramente al pivote P. Un bloque de 600 kg está suspendido en el extremo del mástil en A. El mástil forma un ángulo de 30 con la horizontal, y está sujetado por un cable, de 4.0 m de largo desde P, y el punto P se localiza 4.0 encima de P. El centro de masa del mástil está en el punto C, que está a 2.0 m de P. En la Figura 11.5, la tensión en el cable corresponde a: A) 8800 N B) 8300 N C) 9000 N D) 7800 N E) 9800 N 5) Figura ) Una escalera uniforme de 80 kg y 5 m de longitud, es colocada sobre una pared lisa a una altura de 3.3 m. La base de la escalera descansa sobre una superficie horizontal rugosa cuyo coeficiente de fricción estática es de Un bloque de 80 kg está suspendido desde el peldaño superior de la escalera, cerca de la pared. En lafigura 11.3, la fuerza ejercida sobre la pared por la escalera corresponde a: A) 1300 N B) 1600 N C) 1200 N D) 1000 N E) 1900 N 6) 7) Two equal forces are applied to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force exerts the greater torque? A) the second at the doorknob B) both exert equal non-zero torques C) both exert zero torques D) the first at the midpoint E) additional information is needed 7)

3 Figura ) Un marco triangular recto ABC, hecho de puntales ligeros, gira libremente en el punto C. El puntal AB se mantiene en una posición horizontal por una cuerda horizontal entre los puntos A y D. El puntal AC tiene una longitud a = 0.5 m y el puntal BC mide b = 0.3 m. Un bloque de masa M = 9 kg está suspendido de una cuerda que pasa através de una polea sin fricción. La cuerda en B forma un ángulo de 30 con la horizontal, así como se muestra. En la Figura 11.2, la tensión en la cuerda horizontal AD corresponde a: A) 44 N B) 76 N C) 150 N D) 100 N E) 90 N 8) Figura ) En la Figura 11.6, una escalera de 200 N de peso y 10 metros de longitud se recarga sobre una pared lisa (no hay fricción en la pared). Un bombero de 600 N de peso sube por la escalera una distancia x. El coeficiente de fricción entre la escalera y el piso es 0.5. Cuál es el valor máximo de x sin que la escalera se deslice? A) 5.00 m B) 8.44 m C) 6.28 m D) 6.04 m E) 3.93 m 9)

4 10) A uniform 1200-N piece of medical apparatus that is 3.5 m long is suspended horizontally by two vertical wires at its ends. A small but dense 550-N weight is placed on the apparatus 2.0 m from one end, as shown in the figure. What are the tensions, A and B, in the two wires? 10) A) A = 8200 N, B = 9000 N B) A = 840 N, B = 910 N C) A = 910 N, B = 840 N D) A = 880 N, B = 880 N E) A = 9000 N, B = 8200 N SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. FIGURE ) An 82.0 kg-diver stands at the edge of a light 5.00-m diving board, which is supported by two pillars 1.60 m apart, as shown in Fig (a) Find the force exerted by pillar A. (b) Find the force exerted by pillar B. 11) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. Figura ) En la Figura 11.8, el tendón de Aquiles aplica una fuerza F = 720 N. Cuál es el torque que ejerce sobre la unión del tobillo? A) 16.2 N m B) 25.9 N m C) 12.2 N m D) 36.0 N m E) 21.2 N m 12)

5 13) An athlete holds a 7.5-kg shot put in his hand with his lower arm horizontal, as shown in the figure. His lower arm has a mass of 2.8 kg and its center of gravity (or center of mass) is 12 cm from 13) the elbow-joint pivot. How much force must the extensor muscle (which is F M in the figure) in the upper arm exert on the lower arm? A) 1000 N B) 100 N C) 1500 N D) 500 N FIGURE ) A force is applied to the end of a 2.0 ft long uniform board weighing 50. lb, in order to keep it horizontal, while it pushes against a wall at the left. If the angle the force makes with the board is 30 in the direction shown in Fig. 8-8, what is the applied force F? A) 58. lb B) 32. lb C) 90. lb D) 50. lb E) 29. lb 14) FIGURE ) A thick uniform beam is balanced on a pivot as shown in Fig where it is in equilibrium. Which type of equilibrium is this and why is it of that type? A) Neutral. A tilt of the beam does not change the torque that is acting on the body and the total torque will remain zero as it is in equilibrium. B) Stable. When the beam tilts slightly to one side, the center of mass moves to the same side resulting in torque that will cause rotational acceleration in the opposite direction of the slight displacement. C) Stable. All equilibria are stable when a single support is below the center of mass. The equilibria are only unstable or neutral when the support is under one corner of the object. D) Unstable. When the beam tilts slightly to one side, the center of mass moves to the same side resulting in torque that will cause further rotation in that direction. E) The type of stability depends on the mass and length of the beam. Until those values are known, the stability cannot be evaluated. 15)

6 SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. FIGURE ) A 100-kg, 12.0-m long uniform beam is supported in equilibrium by two fulcrums as shown in Fig The left fulcrum is 1.00 m from the nearer end of the beam and the right fulcrum is 3.00 m from the nearer end of the beam. (a) What is the magnitude of the force of the left fulcrum on the beam? (b) What is the magnitude of the force of the right fulcrum on the beam? 16) 17) As shown in the figure, a 10.0 m long bar is attached by a frictionless hinge to a wall and held horizontal by a light rope that makes an angle = 49 with the bar. The bar is uniform and weighs 66.5 N. What distance x from the hinge should a 10.0 kg mass be suspended for the tension in the rope to be 177 N? 17) 18) A uniform ladder 12 meters long rests against a vertical frictionless wall, as shown in the figure. The ladder weighs 400 N and makes an angle = 51 with the floor. A man weighing 874 N climbs slowly up the ladder. When he is 78 m from the bottom of the ladder, it just starts to slip. What is the coefficient of static friction between the floor and the ladder? 18)

7 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 19) A store's sign has a mass of 20 kg and is 3.0 m long. It is uniform, so its center of gravity is at the center of the sign. It is supported horizontally by a small loose bolt attached to the wall at one end and by a wire at the other end, as shown in the figure. What is the tension in the wire? 19) A) 120 N B) 460 N C) 300 N D) 230 N E) 200 N