Question 1

The center of gravity coincides with the center of mass:

Accepted Answer

A)  always 
B)  never 
C)  if the center of mass is at the geometrical center of the body 
D)  if the acceleration due to gravity is uniform over the body 
E)  if the body has a uniform distribution of mass 
A)  always 
B)  never 
C)  if the center of mass is at the geometrical center of the body 
D)  if the acceleration due to gravity is uniform over the body 
E)  if the body has a uniform distribution of mass D

Question 2

A 5.0 m weightless strut, hinged to a wall, is used to support an 800-N block as shown. The horizontal and vertical components of the force of the hinge on the strut are:

Accepted Answer

A)  FH = 800 N, FY = 800 N 
B)  FH = 600 N, FY = 800 N 
C)  FH = 800 N, FY = 600 N 
D)  FH = 1200 N, FY = 800 N 
E)  FH = 0 N, FY = 800 N 
A)  FH = 800 N, FY = 800 N 
B)  FH = 600 N, FY = 800 N 
C)  FH = 800 N, FY = 600 N 
D)  FH = 1200 N, FY = 800 N 
E)  FH = 0 N, FY = 800 N B

Question 3

The diagram shows a stationary 5-kg uniform rod (AC), 1 m long, held against a wall by a rope (AE) and friction between the rod and the wall. To use a single equation to find the force exerted on the rod by the rope at which point should you place the reference point for computing torque?

Accepted Answer

A)  A 
B)  B 
C)  C 
D)  D 
E)  E 
A)  A 
B)  B 
C)  C 
D)  D 
E)  E C

Question 4

A 960-N block is suspended as shown. The beam AB is weightless and is hinged to the wall at A. The tension force of the cable BC has magnitude:

Accepted Answer

A)  720 N 
B)  1200 N 
C)  1280 N 
D)  1600 N 
E)  none of these 
A)  720 N 
B)  1200 N 
C)  1280 N 
D)  1600 N 
E)  none of these

Question 5

A certain wire stretches 0.90 cm when outward forces with magnitude F are applied to each end. The same forces are applied to a wire of the same material but with three times the diameter and three times the length. The second wire stretches:

Accepted Answer

A)  0.10 cm 
B)  0.30 cm 
C)  0.90 cm 
D)  2.7 cm 
E)  8.1 cm 
A)  0.10 cm 
B)  0.30 cm 
C)  0.90 cm 
D)  2.7 cm 
E)  8.1 cm

Question 6

Which of the following is in static equilibrium?

Accepted Answer

A)  a rock resting on the ground 
B)  a rock sliding at constant velocity across a frictionless surface 
C)  a rock rotating in place on a frictionless surface 
D)  a rock rotating at a constant rate as it slides at constant velocity across a frictionless surface 
E)  a rock falling off a cliff 
A)  a rock resting on the ground 
B)  a rock sliding at constant velocity across a frictionless surface 
C)  a rock rotating in place on a frictionless surface 
D)  a rock rotating at a constant rate as it slides at constant velocity across a frictionless surface 
E)  a rock falling off a cliff

Question 7

Young's modulus can be used to calculate the strain for a stress that is:

Accepted Answer

A)  just below the ultimate strength 
B)  just above the ultimate strength 
C)  well below the yield strength 
D)  well above the yield strength 
E)  none of the above 
A)  just below the ultimate strength 
B)  just above the ultimate strength 
C)  well below the yield strength 
D)  well above the yield strength 
E)  none of the above

Question 8

The uniform rod shown below is held in place by the rope and wall. Suppose you know the weight of the rod and all dimensions. Then you can solve a single equation for the force exerted by the rope, provided you write expressions for the torques about the point:

Accepted Answer

A)  1 
B)  2 
C)  3 
D)  4 
E)  1, 2, or 3 
A)  1 
B)  2 
C)  3 
D)  4 
E)  1, 2, or 3

Question 9

A uniform plank XY is supported by two equal 120-N forces at X and Y, as shown. The support at X is then moved to Z (half-way to the plank center). The supporting forces at Y and Z are then:

Accepted Answer

A)  FY = 240 N, FZ = 120 N 
B)  FY = 200 N, FZ = 40 N 
C)  FY = 40 N, FZ = 200 N 
D)  FY = 80 N, FZ = 160 N 
E)  FY = 160 N, FZ = 80 N 
A)  FY = 240 N, FZ = 120 N 
B)  FY = 200 N, FZ = 40 N 
C)  FY = 40 N, FZ = 200 N 
D)  FY = 80 N, FZ = 160 N 
E)  FY = 160 N, FZ = 80 N

Question 10

A ladder leans against a wall. If the ladder is not to slip, which one of the following must be true?

Accepted Answer

A)  The coefficient of friction between the ladder and the wall must not be zero 
B)  The coefficient of friction between the ladder and the floor must not be zero 
C)  Both A and B 
D)  Either A or B 
E)  Neither A nor B 
A)  The coefficient of friction between the ladder and the wall must not be zero 
B)  The coefficient of friction between the ladder and the floor must not be zero 
C)  Both A and B 
D)  Either A or B 
E)  Neither A nor B

Question 11

To determine if a rigid body is in equilibrium the vector sum of the gravitational forces acting on the particles of the body can be replaced by a single force acting at:

Accepted Answer

A)  the center of mass 
B)  the geometrical center 
C)  the center of gravity 
D)  a point on the boundary 
E)  none of the above 
A)  the center of mass 
B)  the geometrical center 
C)  the center of gravity 
D)  a point on the boundary 
E)  none of the above

Question 12

Young's modulus can be correctly given in:

Accepted Answer

A)  N.m 
B)  N.m2 
C)  N.m/s 
D)  N/m 
E)  joules 
A)  N.m 
B)  N.m2 
C)  N.m/s 
D)  N/m 
E)  joules

Question 13

A 240-N weight is hung from two ropes as shown. The tension in the horizontal rope has magnitude:

Accepted Answer

A)  0 N 
B)  660 N 
C)  480 N 
D)  420 N 
E)  140 N 
A)  0 N 
B)  660 N 
C)  480 N 
D)  420 N 
E)  140 N

Question 14

Which of the following is NOT in equilibrium?

Accepted Answer

A)  a rock resting on the ground 
B)  a rock sliding at constant velocity across a frictionless surface 
C)  a rock rotating in place on a frictionless surface 
D)  a rock rotating at a constant rate as it slides at constant velocity across a frictionless surface 
E)  a rock falling off a cliff 
A)  a rock resting on the ground 
B)  a rock sliding at constant velocity across a frictionless surface 
C)  a rock rotating in place on a frictionless surface 
D)  a rock rotating at a constant rate as it slides at constant velocity across a frictionless surface 
E)  a rock falling off a cliff

Question 15

A uniform 240-g meter stick can be balanced by a 240-g weight placed at the 100-cm mark if the fulcrum is placed at the point marked:

Accepted Answer

A)  75 cm 
B)  60 cm 
C)  50 cm 
D)  40 cm 
E)  80 cm 
A)  75 cm 
B)  60 cm 
C)  50 cm 
D)  40 cm 
E)  80 cm

Question 16

A picture P of weight W is hung by two strings as shown. The magnitude of the tension force of each string is T. The total upward pull of the strings on the picture is:

Accepted Answer

A)  2W cos $\theta$ 
B)  T sin $\theta$ 
C)  T cos $\theta$ 
D)  2T sin $\theta$ 
E)  2T cos$\theta$ 
A)  2W cos $\theta$ 
B)  T sin $\theta$ 
C)  T cos $\theta$ 
D)  2T sin $\theta$ 
E)  2T cos$\theta$

Question 17

A shearing force of 50 N is applied to an aluminum rod with a length of 10 m, a cross-sectional area of 1.0 *10 - 5 m, and shear modulus of 2.5 *1010 N/m2. As a result the rod is sheared through a distance of:

Accepted Answer

A)  zero 
B)  2.0 mm 
C)  2.0 cm 
D)  20 cm 
E)  2.0 m 
A)  zero 
B)  2.0 mm 
C)  2.0 cm 
D)  20 cm 
E)  2.0 m

Question 18

Young's modulus is a proportionality constant that relates the force per unit area applied perpendicularly at the surface of an object to:

Accepted Answer

A)  the shear 
B)  the fractional change in volume 
C)  the fractional change in length 
D)  the pressure 
E)  the spring constant 
A)  the shear 
B)  the fractional change in volume 
C)  the fractional change in length 
D)  the pressure 
E)  the spring constant

Question 19

A 4.0 m steel beam with a cross sectional area of 1.0 * 10-2 m2 and a Young's modulus of 2.0 * 1011 N/m2 is wedged horizontally between two vertical walls. In order to wedge the beam, it is compressed by 0.020 mm. If the coefficient of static friction between the beam and the walls is 0.35, the maximum mass (including its own) it can bear without slipping is:

Accepted Answer

A)  0 kg 
B)  36 kg 
C)  70 kg 
D)  360 kg 
E)  700 kg 
A)  0 kg 
B)  36 kg 
C)  70 kg 
D)  360 kg 
E)  700 kg

Question 20

Three identical uniform rods are each acted on by two or more forces, all perpendicular to the rods. Which of the rods could be in static equilibrium if an additional force is applied at the center of mass of the rod?

Accepted Answer

A)  Only 1 
B)  Only 2 
C)  Only 3 
D)  Only 1 and 2 
E)  All three 
A)  Only 1 
B)  Only 2 
C)  Only 3 
D)  Only 1 and 2 
E)  All three

Exam 12: Equilibrium and Elasticity

The center of gravity coincides with the center of mass:

A 5.0 m weightless strut, hinged to a wall, is used to support an 800-N block as shown. The horizontal and vertical components of the force of the hinge on the strut are:

The diagram shows a stationary 5-kg uniform rod (AC), 1 m long, held against a wall by a rope (AE) and friction between the rod and the wall. To use a single equation to find the force exerted on the rod by the rope at which point should you place the reference point for computing torque?

A 960-N block is suspended as shown. The beam AB is weightless and is hinged to the wall at A. The tension force of the cable BC has magnitude:

A certain wire stretches 0.90 cm when outward forces with magnitude F are applied to each end. The same forces are applied to a wire of the same material but with three times the diameter and three times the length. The second wire stretches:

Which of the following is in static equilibrium?

Young's modulus can be used to calculate the strain for a stress that is:

The uniform rod shown below is held in place by the rope and wall. Suppose you know the weight of the rod and all dimensions. Then you can solve a single equation for the force exerted by the rope, provided you write expressions for the torques about the point:

A uniform plank XY is supported by two equal 120-N forces at X and Y, as shown. The support at X is then moved to Z (half-way to the plank center). The supporting forces at Y and Z are then:

A ladder leans against a wall. If the ladder is not to slip, which one of the following must be true?

To determine if a rigid body is in equilibrium the vector sum of the gravitational forces acting on the particles of the body can be replaced by a single force acting at:

Young's modulus can be correctly given in:

A 240-N weight is hung from two ropes as shown. The tension in the horizontal rope has magnitude:

Which of the following is NOT in equilibrium?

A uniform 240-g meter stick can be balanced by a 240-g weight placed at the 100-cm mark if the fulcrum is placed at the point marked:

A picture P of weight W is hung by two strings as shown. The magnitude of the tension force of each string is T. The total upward pull of the strings on the picture is:

A shearing force of 50 N is applied to an aluminum rod with a length of 10 m, a cross-sectional area of 1.0 *10 - 5 m, and shear modulus of 2.5 *1010 N/m2. As a result the rod is sheared through a distance of:

Young's modulus is a proportionality constant that relates the force per unit area applied perpendicularly at the surface of an object to:

Three identical uniform rods are each acted on by two or more forces, all perpendicular to the rods. Which of the rods could be in static equilibrium if an additional force is applied at the center of mass of the rod?

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A shearing force of 50 N is applied to an aluminum rod with a length of 10 m, a cross-sectional area of 1.0 10 ^- ⁵ m, and shear modulus of 2.5 10¹⁰N/m².As a result the rod is sheared through a distance of: