Chapter 12_Static Equilibrium and Elasticity

Daniel and Jonathan are playing on the seesaw in the park. The 6-m long uniform board is hinged at its midpoint. If Daniel and Jonathan weigh 30 and 20 kg and sit at distances of 2 and 3 m, respectively, from the fulcrum, calculate where their mother (mass = 60 kg) has to sit on the other side of the fulcrum for static equilibrium. A.2.0 m B. 1.5 m C. 1.0 m D. 2.5 m E.None of the above

A.2.0 m

A meter stick is put on a fulcrum at 40 cm mark. When a mass of 100 g is suspended at 10 cm mark on the left of the pivot point, the meter stick is perfectly balanced. The center of gravity of the meter stick is at 50 cm mark. What is the mass of the meter stick? A.300 g B.100 g C.50 g D.40 g E.200 g

A.300 g

The elasticity of a material is characterized by the value of A.the elastic constant. B. Young's modulus. C. the spring constant. D. Hooke's modulus. E. the strain modulus.

B. Young's modulus.

The point that identifies the proportional limit of the material whose graph of stress as a function of strain is shown below is A.1 B.2 C.3 D.4 E.5

B.2

A uniform 325 N ladder rests against a smooth wall, making angle 52° with the wall. The normal force that the wall exerts on the ladder is, A.532 N B.208 N C.163 N D.325 N E.87.5 N

B.208 N

The horizontal bar in the figure will remain horizontal if A. L1 = L2 and R1 = R2 B. L1 = L2 and M1 = M2 C. R1 = R2 and M1 = M2 D. L1M1 = L2M2 E. R1L1 = R2L2

C. R1 = R2 and M1 = M2

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is A.1/4 kg B.1/2 kg C.1 kg D.3/4 kg E.None of the above

C.1 kg

A uniform 3.8 kg board serves as a seesaw for two children. The first child has a mass of 55 kg and sits 2.8 m to the left of the fulcrum. The second child has a mass of 44 kg and sits to the right of the fulcrum. The fulcrum is placed under the center of gravity of the board. How far from the fulcrum the second child should sit to balance the system? A.3.0 m B.4.0 m C.3.5 m D.2.5 m E.2.0 m

C.3.5 m

A 70 kg mountain climber dangling in a crevasse stretches a 50-m-long, 1.0-cm-diameter rope by 8.0 cm. What is Young's modulus for the rope? A.2.48×107 N/m2 B.1.36×108 N/m2 C.5.46×109 N/m2 D.3.12×109 N/m2 E.8.15×106 N/m2

C.5.46×109 N/m2

Under which of the following conditions can a ladder standing on a frictionless horizontal floor and leaning against a rough vertical wall be in equilibrium? A.The normal force exerted by the floor on the ladder equals the normal force the wall exerts on the ladder. B.The weight of the ladder is equal in magnitude to the frictional force the wall exerts on the ladder. C.A ladder in this situation cannot be in equilibrium. D.The normal force exerted by the floor on the ladder equals the weight of the ladder. E.The normal force exerted by the floor on the ladder equals the frictional force the wall exerts on the ladder.

C.A ladder in this situation cannot be in equilibrium.

For a rigid body to remain in equilibrium it is necessary and sufficient that A.E F=0 B.E Ia=0 C.E T=0; E f=0 D.E T=0 E.E mr=0

C.E T=0; E f=0

A 10-m=long plank (of negligible mass) is supported at each end by vertical cables, also of negligible mass. A person of unknown weight sits on the plank between the cables. The tension in the left cable is 300 N, and in the right cable it is 200 N. The person's weight is A.100 N B. 300 N C. 400 N D. 500 N E.700 N

D. 500 N

A 6 cm long ruler, balanced at its center point, has two coins placed on it, as shown in the figure. One coin, of mass M1=10g, is placed at the zero mark; the other, of unknown mass M2, is placed at the 4.7 cm mark. The center of the ruler is at the 3.0 cm mark. The ruler is in equilibrium; it is perfectly balanced. Calculate the value of M2. A.10 g B. 28 g C. 8 g D.18 g E. 48 g

D.18 g

An object could not be in static equilibrium under which of the following conditions? A.when only one force is acting on it. B.when only one torque is acting on it. C.if it is rotating with constant angular speed. D.all of them.

D.all of them.

A body is in translational equilibrium when A.it is acted on by a constant force. B.no friction forces are involved. C.it has a constant acceleration. D.it has a constant velocity. E.no contact forces are involved.

D.it has a constant velocity.

Young's modulus Y has units of A.force. B.mass density. C.energy. D.pressure. E.mass per unit time.

D.pressure.

An 80-cm-long, 1.0-mm-diameter steel guitar string must be tightened to a tension of 2000 N by turning the tuning screws. By how much is the string stretched? Young's Modulus of elasticity for steel = 20×1010 N/m2 A.5.12 cm B.3.48 cm C.8.04 cm D.2.42 cm E.1.02 cm

E.1.02 cm

An object has the following two conditions, SF = 0 and St = 0. Which of the following statements can be true? A.The object is at rest. B.The object is moving at a constant velocity and rotating with a constant angular velocity. C.The object is moving at a constant velocity but is not rotating. D.The object does not have a translation motion but is rotating at a constant angular velocity. E.All of the above.

E.All of the above.

A body is in mechanical equilibrium when A.it is moving with constant acceleration. B.it is being moved by a constant force. C.the sum of the external forces acting on it is zero. D.the sum of the external torques acting on it is zero. E.it is moving with constant linear velocity and rotating with a constant angular velocity.

E.it is moving with constant linear velocity and rotating with a constant angular velocity.

Which of the following could not have units of N/m2? A.Young's modulus B.shear modulus C.bulk modulus D.stress E.strain

E.strain