Question 1

If the sum of the external forces on an object is zero, then the sum of the external torques on it must also be zero.

Accepted Answer

A) True 
 B)False  False

Question 2

Which of the following are SI units of Young's modulus? (There could be more than one correct choice.)

Accepted Answer

A)  N/m ∙ s2 
B)  kg/m2 
C)  kg ∙ m/s2 
D)  kg/m ∙ s2 
E)  kg ∙ m2/s2 
A)  N/m ∙ s2 
B)  kg/m2 
C)  kg ∙ m/s2 
D)  kg/m ∙ s2 
E)  kg ∙ m2/s2 D

Question 3

A 25-kg piece of equipment can be hung by steel wires of length 1.00 m, 2.00 m, or 3.00 m. If all the wires have the same diameter, which one will stretch the greatest percent?

Accepted Answer

A)  the 1.00-m wire 
B)  the 2.00-m wire 
C)  the 3.00-m wire 
D)  They will all stretch by the same percent. 
A)  the 1.00-m wire 
B)  the 2.00-m wire 
C)  the 3.00-m wire 
D)  They will all stretch by the same percent. D

Question 4

A brass wire 2.0 m long and 2.0 mm in diameter supports a 10.0-kg fixture. By what distance did this fixture stretch the wire? Young's modulus for brass is 10 × 1010 N/m2.

Accepted Answer

A)  0.11 mm 
B)  0.22 mm 
C)  0.33 mm 
D)  0.62 mm 
A)  0.11 mm 
B)  0.22 mm 
C)  0.33 mm 
D)  0.62 mm

Question 5

If the sum of the external torques on an object is zero, then the sum of the external forces on it must also be zero.

Accepted Answer

A) True 
 B)False

Question 6

A child is trying to stack two uniform bricks, each 24 cm long, so they will protrude as far as possible over the edge of a table without tipping over, as shown in the figure. What is the maximum possible overhang distance d?

Accepted Answer

A)  10 cm 
B)  12 cm 
C)  14 cm 
D)  16 cm 
E)  18 cm 
A)  10 cm 
B)  12 cm 
C)  14 cm 
D)  16 cm 
E)  18 cm

Question 7

A steel wire, 3.2 m long, has a diameter of 1.2 mm. The wire stretches 1.6 mm when it bears a load. Young's modulus for steel is 2.0 × 1011 Pa. The mass of the load is closest to

Accepted Answer

A)  12 kg. 
B)  16 kg. 
C)  20 kg. 
D)  24 kg. 
E)  28 kg. 
A)  12 kg. 
B)  16 kg. 
C)  20 kg. 
D)  24 kg. 
E)  28 kg.

Question 8

To determine the location of the center of mass (or center of gravity) of a car, the car is driven over a scale on a horizontal floor. When the front wheels are over the scale, the weight recorded by the scale is 5800 N, and when the rear wheels are over the scale, the scale reads 6500 N. The distance between the front and rear wheels is measured to be 3.20 m. How far behind the front wheels is the center of mass located?

Accepted Answer

A)  0.845 m 
B)  1.50 m 
C)  1.59 m 
D)  1.69 m 
E)  1.72 m 
A)  0.845 m 
B)  1.50 m 
C)  1.59 m 
D)  1.69 m 
E)  1.72 m

Question 9

An aluminum wire and a steel wire, each of length 2.0 m, are hung from the ceiling. A 5.0-kg mass is suspended from the lower end of each wire. The aluminum wire has a diameter of 2.2 mm. What must be the diameter of the steel wire if it is to stretch the same distance as the aluminum wire, so that the two wires maintain equal lengths after the masses are attached? Young's modulus for aluminum is 0.70 × 1011 Pa and for steel it is 2.0 × 1011 Pa.

Accepted Answer

Question 10

A piano wire has a radius of 0.50 mm. One end is fixed and the other is wrapped around a tuning peg, which has a diameter of 3.5 mm and is 80 cm away. After the wire just becomes taut, the peg is given three full turns. What is the tension in the wire? Young's modulus for steel is 2.0 × 1011 N/m2.

Accepted Answer

A)  3.8 kN 
B)  4.3 kN 
C)  6.5 kN 
D)  8.7 kN 
E)  9.8 kN 
A)  3.8 kN 
B)  4.3 kN 
C)  6.5 kN 
D)  8.7 kN 
E)  9.8 kN

Question 11

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 θ = 49° with the bar. The bar is uniform and weighs $66.5 \mathrm {~N}$ What distance x from the hinge should a 10.0 kg mass be suspended for the tension in the rope to be 177 N?

Accepted Answer

The answer of As shown in the figure, a 10.0...

Question 12

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?

Accepted Answer

A)  460 N 
B)  230 N 
C)  120 N 
D)  200 N 
E)  300 N 
A)  460 N 
B)  230 N 
C)  120 N 
D)  200 N 
E)  300 N

Question 13

A wire that is 1.0 mm in diameter and 3.5 m long stretches 3.5 mm when an 8.0-kg tool is hung from it.
(a) What is Young's modulus for the material from this wire is made?
(b) What is the effective spring constant for the stretching wire?

Accepted Answer

(a) 1.0 ×

Question 14

If the sum of both the external torques and the external forces on an object is zero, then the object must be at rest.

Accepted Answer

A) True 
 B)False

Question 15

A 100-kg nonuniform boom that is 6.0 m long is loosely pinned at the pivot at P. A 600-kg concrete block is suspended from the end of the boom at A, as shown in the figure. The boom forms a 30° angle above the horizontal, and is supported by a 4.0-m cable between points D and B. Point B is 4.0 m from P, and point D is 4.0 m above P. The center of mass of the boom is at point C, which is 2.0 m from P. Assume that all the quantities shown in the figure are accurate to two significant figures. What is the tension in the cable connected between points B and D?

Accepted Answer

A)  9300 N 
B)  8400 N 
C)  8100 N 
D)  7500 N 
E)  6900 N 
A)  9300 N 
B)  8400 N 
C)  8100 N 
D)  7500 N 
E)  6900 N

Question 16

A 5.00-m-long uniform ladder, weighing 200 N, rests against a smooth vertical wall with its base on a horizontal rough floor, a distance of 1.20 m away from the wall. The coefficient of static friction between the ladder and the floor is 0.200. How far up the ladder, measured along the ladder, can a 600-N person climb before the ladder begins to slip?

Accepted Answer

A)  1.50 m 
B)  1.26 m 
C)  1.05 m 
D)  3.95 m 
E)  4.56 m 
A)  1.50 m 
B)  1.26 m 
C)  1.05 m 
D)  3.95 m 
E)  4.56 m

Question 17

A wire of diameter 0.20 mm stretches by 0.20% when a 6.28-N force is applied to it. What is Young's modulus for this wire?

Accepted Answer

A)  2.5 × 1010 Pa 
B)  1.0 × 1011 Pa 
C)  2.5 × 1012 Pa 
D)  1.0 ×1012 Pa 
A)  2.5 × 1010 Pa 
B)  1.0 × 1011 Pa 
C)  2.5 × 1012 Pa 
D)  1.0 ×1012 Pa

Question 18

Which one of the following is an accurate statement?

Accepted Answer

A)  The ratio of tensile stress to tensile strain is called Young's modulus. 
B)  "Strain" has a meaning very close to "force." 
C)  "Stress" has a meaning very close to "stretch." 
D)  Tensile stress is measured in newtons. 
E)  Tensile strain is measured in meters. 
A)  The ratio of tensile stress to tensile strain is called Young's modulus. 
B)  "Strain" has a meaning very close to "force." 
C)  "Stress" has a meaning very close to "stretch." 
D)  Tensile stress is measured in newtons. 
E)  Tensile strain is measured in meters.

Question 19

A large 75-kg lighting fixture can be hung from wires of identical size and shape made of aluminum, brass, or copper. The values of Young's modulus for these metals are 0.70 × 1011 Pa (aluminum), 0.91 × 1011 (brass), and 1.1 × 1011 (copper). Which wire would stretch the least distance?

Accepted Answer

A)  aluminum 
B)  brass 
C)  copper 
D)  They will all stretch the same distance. 
A)  aluminum 
B)  brass 
C)  copper 
D)  They will all stretch the same distance.

Question 20

The graph in the figure shows the tensile stress as a function of the tensile strain in a certain wire. What does the slope of this graph give us for this wire?

Accepted Answer

A)  the pressure in the wire 
B)  Young's modulus for the material of the wire 
C)  the tensile stress in the wire 
D)  the tension in the wire 
E)  the percent change in the length of the wire 
A)  the pressure in the wire 
B)  Young's modulus for the material of the wire 
C)  the tensile stress in the wire 
D)  the tension in the wire 
E)  the percent change in the length of the wire

Exam 8: Equilibrium Ad Elasticity

If the sum of the external forces on an object is zero, then the sum of the external torques on it must also be zero.

Which of the following are SI units of Young's modulus? (There could be more than one correct choice.)

A 25-kg piece of equipment can be hung by steel wires of length 1.00 m, 2.00 m, or 3.00 m. If all the wires have the same diameter, which one will stretch the greatest percent?

A brass wire 2.0 m long and 2.0 mm in diameter supports a 10.0-kg fixture. By what distance did this fixture stretch the wire? Young's modulus for brass is 10 × 1010 N/m2.

If the sum of the external torques on an object is zero, then the sum of the external forces on it must also be zero.

A child is trying to stack two uniform bricks, each 24 cm long, so they will protrude as far as possible over the edge of a table without tipping over, as shown in the figure. What is the maximum possible overhang distance d?

A steel wire, 3.2 m long, has a diameter of 1.2 mm. The wire stretches 1.6 mm when it bears a load. Young's modulus for steel is 2.0 × 1011 Pa. The mass of the load is closest to

A piano wire has a radius of 0.50 mm. One end is fixed and the other is wrapped around a tuning peg, which has a diameter of 3.5 mm and is 80 cm away. After the wire just becomes taut, the peg is given three full turns. What is the tension in the wire? Young's modulus for steel is 2.0 × 1011 N/m2.

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?

A wire that is 1.0 mm in diameter and 3.5 m long stretches 3.5 mm when an 8.0-kg tool is hung from it. (a) What is Young's modulus for the material from this wire is made? (b) What is the effective spring constant for the stretching wire?

If the sum of both the external torques and the external forces on an object is zero, then the object must be at rest.

A wire of diameter 0.20 mm stretches by 0.20% when a 6.28-N force is applied to it. What is Young's modulus for this wire?

Which one of the following is an accurate statement?

A large 75-kg lighting fixture can be hung from wires of identical size and shape made of aluminum, brass, or copper. The values of Young's modulus for these metals are 0.70 × 1011 Pa (aluminum), 0.91 × 1011 (brass), and 1.1 × 1011 (copper). Which wire would stretch the least distance?

The graph in the figure shows the tensile stress as a function of the tensile strain in a certain wire. What does the slope of this graph give us for this wire?

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A brass wire 2.0 m long and 2.0 mm in diameter supports a 10.0-kg fixture. By what distance did this fixture stretch the wire? Young's modulus for brass is 10 × 10¹⁰ N/m².

A steel wire, 3.2 m long, has a diameter of 1.2 mm. The wire stretches 1.6 mm when it bears a load. Young's modulus for steel is 2.0 × 10¹¹ Pa. The mass of the load is closest to

A large 75-kg lighting fixture can be hung from wires of identical size and shape made of aluminum, brass, or copper. The values of Young's modulus for these metals are 0.70 × 10¹¹ Pa (aluminum), 0.91 × 10¹¹ (brass), and 1.1 × 10¹¹ (copper). Which wire would stretch the least distance?