Question 1

Strain can be measured in:

Accepted Answer

A)  N/m2 
B)  N.m2 
C)  N/m 
D)  N.m 
E)  none of these (it is unitless) 
A)  N/m2 
B)  N.m2 
C)  N/m 
D)  N.m 
E)  none of these (it is unitless) E

Question 2

A picture can be hung on a wall in three different ways, as shown. The tension in the string is:

Accepted Answer

A)  least in I 
B)  greatest in I 
C)  greatest in II 
D)  least in III 
E)  greatest in III 
A)  least in I 
B)  greatest in I 
C)  greatest in II 
D)  least in III 
E)  greatest in III E

Question 3

For an object in equilibrium the sum of the torques acting on it vanishes only if each torque is calculated about:

Accepted Answer

A)  the center of mass 
B)  the center of gravity 
C)  the geometrical center 
D)  the point of application of the force 
E)  the same point 
A)  the center of mass 
B)  the center of gravity 
C)  the geometrical center 
D)  the point of application of the force 
E)  the same point E

Question 4

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

Question 5

A cylinder placed so it can roll on a horizontal table top, with its center of gravity above its geometrical center, is:

Accepted Answer

A)  in stable equilibrium 
B)  in unstable equilibrium 
C)  in neutral equilibrium 
D)  not in equilibrium 
E)  none of the above 
A)  in stable equilibrium 
B)  in unstable equilibrium 
C)  in neutral equilibrium 
D)  not in equilibrium 
E)  none of the above

Question 6

A uniform plank is 6.0 m long and weighs 80 N. It is balanced on a sawhorse at its center. An additional 160 N weight is now placed on the left end of the plank. To keep the plank balanced, it must be moved what distance to the right?

Accepted Answer

A)  6.0 m 
B)  2.0 m 
C)  1.5 m 
D)  1.0 m 
E)  0.50 m 
A)  6.0 m 
B)  2.0 m 
C)  1.5 m 
D)  1.0 m 
E)  0.50 m

Question 7

A cylinder placed so it can roll on a horizontal table top, with its center of gravity below its geometrical center, is:

Accepted Answer

A)  in stable equilibrium 
B)  in unstable equilibrium 
C)  in neutral equilibrium 
D)  not in equilibrium 
E)  none of the above 
A)  in stable equilibrium 
B)  in unstable equilibrium 
C)  in neutral equilibrium 
D)  not in equilibrium 
E)  none of the above

Question 8

A force of 5000 N is applied outwardly to each end of a 5.0-m long rod with a radius of 34.0 cm and a Young's modulus of 125 * 108 N/m2. The elongation of the rod is:

Accepted Answer

A)  0.0020 mm 
B)  0.0040 mm 
C)  0.14 mm 
D)  0.55 mm 
E)  1.42 mm 
A)  0.0020 mm 
B)  0.0040 mm 
C)  0.14 mm 
D)  0.55 mm 
E)  1.42 mm

Question 9

The ideal mechanical advantage (i.e. the ratio of the weight W to the pull P for equilibrium) of the combination of pulleys shown is:

Accepted Answer

A)  1 
B)  2 
C)  3 
D)  4 
E)  5 
A)  1 
B)  2 
C)  3 
D)  4 
E)  5

Question 10

The 600-N ball shown is suspended on a string AB and rests against the frictionless vertical wall. The string makes an angle of 30$\degree$with the wall. The magnitude of the tension for of string is:

Accepted Answer

A)  690 N 
B)  1200 N 
C)  2100 N 
D)  2400 N 
E)  none of these 
A)  690 N 
B)  1200 N 
C)  2100 N 
D)  2400 N 
E)  none of these

Question 11

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 12

A 5.0 m weightless strut, hinged to a wall, is used to support a 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 , 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 , FY = 800 N

Question 13

A cube balanced with one edge in contact with a table top and with its center of gravity directly above the edge is in ________ equilibrium with respect to rotation about the edge and in ________ equilibrium with respect to rotation about a horizontal axis that is perpendicular to the edge.

Accepted Answer

A)  stable, stable 
B)  stable, unstable 
C)  unstable, stable 
D)  unstable, unstable 
E)  unstable, neutral 
A)  stable, stable 
B)  stable, unstable 
C)  unstable, stable 
D)  unstable, unstable 
E)  unstable, neutral

Question 14

A uniform rod AB is 1.2 m long and weighs 16 N. It is suspended by strings AC and BD as shown. A block P weighing 96 N is attached at E, 0.30 m from A. The magnitude of the tension force in the string BD is:

Accepted Answer

A)  8.0 N 
B)  24 N 
C)  32 N 
D)  48 N 
E)  80 N 
A)  8.0 N 
B)  24 N 
C)  32 N 
D)  48 N 
E)  80 N

Question 15

A meter stick on a horizontal frictionless table top is pivoted at the 80-cm mark. A force   is applied perpendicularly to the end of the stick at 0 cm, as shown. A second force   (not shown) is applied perpendicularly at the 100-cm end of the stick. The forces are horizontal. If the stick does not move, the force exerted by the pivot on the stick:

Accepted Answer

A)  must be zero 
B)  must be in the same direction as   and have magnitude   
C)  must be directed opposite to   and have magnitude   
D)  must be in the same direction as   and have magnitude   
E)  must be directed opposite to   and have magnitude   
A)  must be zero 
B)  must be in the same direction as   and have magnitude   
C)  must be directed opposite to   and have magnitude   
D)  must be in the same direction as   and have magnitude   
E)  must be directed opposite to   and have magnitude

Question 16

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 17

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 18

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 19

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 20

Two supports, made of the same material and initially of equal length, are 2.0 m apart. A stiff board with a length of 4.0 m and a mass of 10 kg is placed on the supports, with one support at the left end and the other at the midpoint. A block is placed on the board a distance of 0.50 m from left end.As a result the board is horizontal. The mass of the block is:

Accepted Answer

A)  zero 
B)  2.3 kg 
C)  6.6 kg 
D)  10 kg 
E)  20 kg 
A)  zero 
B)  2.3 kg 
C)  6.6 kg 
D)  10 kg 
E)  20 kg

Exam 12: Equilibrium and Elasticity

Strain can be measured in:

A picture can be hung on a wall in three different ways, as shown. The tension in the string is:

For an object in equilibrium the sum of the torques acting on it vanishes only if each torque is calculated about:

The center of gravity coincides with the center of mass:

A cylinder placed so it can roll on a horizontal table top, with its center of gravity above its geometrical center, is:

A uniform plank is 6.0 m long and weighs 80 N. It is balanced on a sawhorse at its center. An additional 160 N weight is now placed on the left end of the plank. To keep the plank balanced, it must be moved what distance to the right?

A cylinder placed so it can roll on a horizontal table top, with its center of gravity below its geometrical center, is:

A force of 5000 N is applied outwardly to each end of a 5.0-m long rod with a radius of 34.0 cm and a Young's modulus of 125 * 108 N/m2. The elongation of the rod is:

The ideal mechanical advantage (i.e. the ratio of the weight W to the pull P for equilibrium) of the combination of pulleys shown is:

The 600-N ball shown is suspended on a string AB and rests against the frictionless vertical wall. The string makes an angle of 30 °\degree° with the wall. The magnitude of the tension for of string is:

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

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

A cube balanced with one edge in contact with a table top and with its center of gravity directly above the edge is in ________ equilibrium with respect to rotation about the edge and in ________ equilibrium with respect to rotation about a horizontal axis that is perpendicular to the edge.

A uniform rod AB is 1.2 m long and weighs 16 N. It is suspended by strings AC and BD as shown. A block P weighing 96 N is attached at E, 0.30 m from A. The magnitude of the tension force in the string BD is:

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

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

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:

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:

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A force of 5000 N is applied outwardly to each end of a 5.0-m long rod with a radius of 34.0 cm and a Young's modulus of 125 * 10⁸ N/m². The elongation of the rod is:

A cube balanced with one edge in contact with a table top and with its center of gravity directly above the edge is in equilibrium with respect to rotation about the edge and in equilibrium with respect to rotation about a horizontal axis that is perpendicular to the edge.