Physics chapter 9 – Flashcards

What condition or conditions are necessary for rotational equilibrium? A) sumFx = 0 B) sumFx = 0, sumT = 0 C) sumT = 0 D) sumFx = 0, sumFy = 0

What condition or conditions are necessary for static equilibrium? A) SFx = 0 B) SFx = 0, SFy = 0, ST = 0 C) ST = 0 D) SFx = 0, SFy = 0

A book weighs 6 N. When held at rest above your head the net force on the book is A) 0 N. B) 6 N. C) 9.8 N. D) -6 N.

A rocket moves through outer space with a constant velocity of 9.8 m/s. What net force acts on it? A) a force equal to its weight on Earth, mg B) a force equal to the gravity acting on it C) The net force is zero. D) cannot be determined without more information

A person weighing 800 N stands with one foot on each of two bathroom scales. Which statement is definitely true? A) Each scale will read 800 N. B) Each scale will read 400 N. C) If one scale reads 500 N, the other will read 300 N. D) None of the above is definitely true.

A heavy boy and a light girl are balanced on a massless seesaw. If they both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw? A) The side the boy is sitting on will tilt downward. B) The side the girl is sitting on will tilt downward. C) Nothing, the seesaw will still be balanced. D) It is impossible to say without knowing the masses and the distances.

Muscles that tend to bring two limbs closer together are called A) tendons. B) flexors. C) extensors. D) insertions.

Muscles that act to extend a limb outward are called A) tendons. B) flexors. C) extensors. D) insertions.

A sphere hanging freely from a cord is in A) stable equilibrium. B) unstable equilibrium. C) neutral equilibrium. D) positive equilibrium.

A cone balanced on its small end is in A) stable equilibrium. B) unstable equilibrium. C) neutral equilibrium. D) positive equilibrium.

A cube resting on a horizontal tabletop is in A) stable equilibrium. B) unstable equilibrium. C) neutral equilibrium. D) positive equilibrium.

12) Consider two identical bricks, each of dimensions 20.0 cm ˛ 10.0 cm ˛ 6.0 cm. One is stacked on the other, and the combination is then placed so that they project out over the edge of a table. What is the maximum distance that the end of the top brick can extend beyond the table edge without toppling? A) 7.5 cm B) 10 cm C) 12.5 cm D) 15 cm

A copper wire is found to break when subjected to minimum tension of 36 N. If the wire diameter were half as great, we would expect the wire to break when subjected to a minimum tension of A) 9.0 N. B) 18 N. C) 36 N. D) 108 N.

A lever is 5.0 m long. The distance from the fulcrum to the weight to be lifted is 1.0 m. If a worker pushes on the opposite end with 400 N, what is the maximum weight that can be lifted? A) 80 N B) 100 N C) 1600 N D) 2000 N

A lever is 5.0 m long. The distance from the fulcrum to the weight to be lifted is 1.0 m. If a 3000 N rock is to be lifted, how much force must be exerted on the lever? A) 600 N B) 750 N C) 3000 N D) 12000 N

A boy and a girl are balanced on a massless seesaw. The boy has a mass of 75 kg and the girl's mass is 50 kg. If the boy sits 2.0 m from the pivot point on one side of the seesaw, where must the girl sit on the other side? A) 1.3 m B) 2.3 m C) 2.5 m D) 3.0 m

Two children sit on opposite ends of a uniform seesaw which pivots in the center. Child A has mass 60 kg and sits 2.0 m from the center. Child B has mass 40 kg. How far from the center must child B sit for the seesaw to balance? A) 1.3 m B) 2.5 m C) 3.0 m D) cannot be determined without knowing the seesaw's mass

A uniform board of weight 40 N supports two children weighing 500 N and 350 N, respectively. If the support is at the center of the board and the 500-N child is 1.5 m from the center, what is the position of the 350-N child? A) 1.1 m B) 1.5 m C) 2.1 m D) 2.7 m

A 10-m uniform beam of weight 100 N is supported by two ropes at the ends. If a 400-N person sits at 2.0 m from the left end of the beam, what is the tension in the left rope? A) 130 N B) 250 N C) 370 N D) 500 N

A 10-m uniform beam of weight 100 N is supported by two ropes at the ends. If a 400-N person sits at 2.0 m from the left end of the beam, what is the tension in the right rope? A) 130 N B) 250 N C) 370 N D) 500 N

A massless scaffold is held up by a wire at each end. The scaffold is 12 m long. A 300-N box sits 4.0 m from the left end. What is the tension in each wire? A) left wire = 100 N; right wire = 200 N B) left wire = 200 N; right wire = 100 N C) left wire = 900 N; right wire = 2700 N D) left wire = 2700 N; right wire = 900 N

A 200-N scaffold is held up by a wire at each end. The scaffold is 18 m long. A 650-N box sits 3.0 m from the left end. What is the tension in each wire? A) left wire = 520 N; right wire = 130 N B) left wire = 640 N; right wire = 210 N C) left wire = 195 N; right wire = 975 N D) left wire = 295 N; right wire = 1000 N

A uniform meter stick is supported by a knife edge at the 50-cm mark and has masses of 0.40 kg and 0.60 kg hanging at the 20-cm and 80-cm marks, respectively. Where (at what mark) should a third mass of 0.30 kg be hung to keep the stick in balance? A) 20 cm B) 25 cm C) 30 cm D) 70 cm

A 500-N person stands on a uniform board of weight 100 N and length 8.0 m. The board is supported at each end. If the support force at the right end is three times that at the left end, how far from the right end is the person? A) 4.0 m B) 2.0 m C) 1.6 m D) 6.4 m

Two scales are separated by 2.00 m, and a plank of mass 4.00 kg is placed between them. Each scale is observed to read 2.00 kg. A person now lies on the plank, after which the right scale reads 30.0 kg and the left scale reads 50.0 kg. How far from the right scale is the person's center of gravity located? A) 1.20 m B) 1.23 m C) 1.26 m D) 1.30 m

Assuming the lower arm has a mass of 2.8 kg and its CG is 12 cm from the elbow-joint pivot, how much force must the extensor muscle in the upper arm exert on the lower arm to hold a 7.5 kg shot put (Fig. 9-1)? A) 100 N B) 500 N C) 1000 N D) 1500 N

A passenger van has an outer wheel base width of 2.00 m. Its center of gravity is equidistant from the sides, and positioned 1.20 m above the ground. What is the maximum sideways angle at which it can be inclined without tipping over? A) 32.6e B) 39.8e C) 50.2e D) 57.3e

The Leaning Tower of Pisa is 55 m tall and about 7.0 m in diameter. The top is 4.5 m off center. How much farther can it lean before it becomes unstable? A) 0.5 m B) 1.5 m C) 2.5 m D) 3.5 m