Question 1

Tensile strain is

Accepted Answer

A)  the ratio of the change in length to the original length. 
B)  the stress per unit area. 
C)  the applied force per unit area. 
D)  the ratio of stress to elastic modulus. 
A)  the ratio of the change in length to the original length. 
B)  the stress per unit area. 
C)  the applied force per unit area. 
D)  the ratio of stress to elastic modulus.

Question 2

A 1200-kg car is being raised with a constant acceleration of 2.53 m/s2 by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0 × 1011 N/m2. What is the change in length of the cable caused by lifting the car?

Accepted Answer

A)  8.4 mm 
B)  8.4 cm 
C)  4.9 mm 
D)  4.9 cm 
E)  4.9 m 
A)  8.4 mm 
B)  8.4 cm 
C)  4.9 mm 
D)  4.9 cm 
E)  4.9 m

Question 3

A uniform 1200-N piece of medical apparatus that is 3.5 m long is suspended horizontally by two vertical wires at its ends. A small but dense 550-N weight is placed on the apparatus 2.0 m from one end, as shown in the figure. What are the tensions, A and B, in the two wires?

Accepted Answer

A)  A = 880 N, B = 880 N 
B)  A = 840 N, B = 910 N 
C)  A = 9000 N, B = 8200 N 
D)  A = 910 N, B = 840 N 
E)  A = 8200 N, B = 9000 N 
A)  A = 880 N, B = 880 N 
B)  A = 840 N, B = 910 N 
C)  A = 9000 N, B = 8200 N 
D)  A = 910 N, B = 840 N 
E)  A = 8200 N, B = 9000 N

Question 4

A light board that is 10 m long is supported by two sawhorses, one at one end of the board and a second at the midpoint. A 40-N weight is placed between the two sawhorses, 3.0 m from the end and 2.0 m from the center. What magnitude forces do the sawhorses exert on the board?

Accepted Answer

16 N at th

Question 5

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

Accepted Answer

A) True 
 B)False

Question 6

A 3.0-kg brick rests on a perfectly smooth ramp inclined at 34° above the horizontal. The brick is kept from sliding down the plane by an ideal spring that is aligned with the surface and attached to a wall above the brick. The spring has a spring constant (force constant) of 120 N/m. By how much does the spring stretch with the brick attached?

Accepted Answer

A)  360 cm 
B)  240 cm 
C)  14 cm 
D)  24 cm 
E)  36 cm 
A)  360 cm 
B)  240 cm 
C)  14 cm 
D)  24 cm 
E)  36 cm

Question 7

A 1200-kg car is being raised at a constant speed if 25 cm/s by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0 × 1011 Pa. What is the change in length of the cable caused by the car?

Accepted Answer

A)  6.7 mm 
B)  6.7 cm 
C)  3.3 mm 
D)  3.3 cm 
E)  3.3 m 
A)  6.7 mm 
B)  6.7 cm 
C)  3.3 mm 
D)  3.3 cm 
E)  3.3 m

Question 8

A stepladder consists of two halves that are hinged at the top and connected by a tie rod which keeps the two halves from spreading apart. In this particular instance, the two halves are 2.5 m long, the tie rod is connected to the center of each half and is 70 cm long. An 800-N person stands 3/5 of the way up the stepladder, as shown in the figure. The ladder is light enough that we can neglect its weight, and it rests on an extremely smooth floor. What is the tension in the tie rod? (Note: To solve this problem, it is helpful to imagine cutting the ladder in half vertically and consider the forces and torques acting on each half of the ladder.)

Accepted Answer

A)  140 N 
B)  240 N 
C)  280 N 
D)  360 N 
E)  560 N 
A)  140 N 
B)  240 N 
C)  280 N 
D)  360 N 
E)  560 N

Question 9

An ornament of mass 40.0 g is attached to a vertical ideal spring with a force constant (spring constant) of 20.0 N/m. The ornament is then lowered very slowly until the spring stops stretching. How much does the spring stretch?

Accepted Answer

A)  0.00200 m 
B)  0.0196 m 
C)  0.0816 m 
D)  0.800 m 
E)  0.200 m 
A)  0.00200 m 
B)  0.0196 m 
C)  0.0816 m 
D)  0.800 m 
E)  0.200 m

Question 10

A light board that is 10 m long is supported by two sawhorses, one at one end of the board and a second at the midpoint. A 40-N object is placed between the two sawhorses, 3.0 m from the end and 2.0 m from the center. A second object, with a weight of 15 N, is placed on the supported end. What magnitude forces do the sawhorses exert on the board?

Accepted Answer

1.0 N at t

Question 11

A 15-kg child is sitting on a playground teeter-totter, 1.5 m from the pivot. What is the magnitude of the minimum force, applied 0.30 m on the other side of the pivot, that is needed to make the child lift off the ground?

Accepted Answer

A)  75 N 
B)  740 N 
C)  23 N 
D)  44 N 
E)  66 N 
A)  75 N 
B)  740 N 
C)  23 N 
D)  44 N 
E)  66 N

Question 12

When a car is weighed, it is driven slowly on a horizontal floor over a scale that records a reading as the front wheels go over the scale, and then records a second reading as the rear wheels go over the scale. The weight of the car is equal to

Accepted Answer

A)  the weight under the front wheels. 
B)  the weight under the rear wheels. 
C)  the average of the two weights. 
D)  the sum of the two weights. 
E)  the difference of the two weights. 
A)  the weight under the front wheels. 
B)  the weight under the rear wheels. 
C)  the average of the two weights. 
D)  the sum of the two weights. 
E)  the difference of the two weights.

Question 13

A 10-m uniform beam weighing 100 N is supported by two vertical ropes at its ends. If a 400-N person sits at a point 2.0 m from the left end of the beam, what is the tension in each rope?

Accepted Answer

370 N (lef

Question 14

An irregularly shaped object that is 10 m long is placed with each end on a scale. If the scale on the right reads $96 \mathrm {~N}$ while the scale on the left reads $71 \mathrm {~N} \text {, }$ how far from the left end is the center of gravity of this object?

Accepted Answer

A)  5.7 m 
B)  7.4 m 
C)  4.3 m 
D)  14 m 
A)  5.7 m 
B)  7.4 m 
C)  4.3 m 
D)  14 m

Question 15

A 120-kg refrigerator that is 2.0 m tall and 85 cm wide has its center of mass at its geometrical center. You are attempting to slide it along the floor by pushing horizontally on the side of the refrigerator. The coefficient of static friction between the floor and the refrigerator is 0.30. Depending on where you push, the refrigerator may start to tip over before it starts to slide along the floor. What is the highest distance above the floor that you can push the refrigerator so that it will not tip before it begins to slide?

Accepted Answer

A)  0.71 m 
B)  1.0 m 
C)  1.2 m 
D)  1.4 m 
E)  1.6 m 
A)  0.71 m 
B)  1.0 m 
C)  1.2 m 
D)  1.4 m 
E)  1.6 m

Question 16

A 50-kg bucket of concrete is suspended from a steel wire that is 1.0 mm in diameter 1.0 mm and 11.2 m long. What distance will the wire stretch? Young's modulus for steel is 2.0 x 1011 Pa.

Accepted Answer

Question 17

An aluminum wire 2.0 m long and 2.0 mm in diameter supports a 10.0-kg fixture. What is the stress in the wire? Young's modulus for aluminum is 7.0 × 1010 N/m2.

Accepted Answer

A)  3.1 × 107 N/m2 
B)  6.2 × 107 N/m2 
C)  9.3 × 107 N/m2 
D)  1.2 × 108 N/m2 
A)  3.1 × 107 N/m2 
B)  6.2 × 107 N/m2 
C)  9.3 × 107 N/m2 
D)  1.2 × 108 N/m2

Question 18

A mobile is shown in the figure. The horizontal supports have negligible mass. Assume that all the numbers given in the figure are accurate to two significant figures. What mass M is required to balance the mobile?

Accepted Answer

A)  18 g 
B)  30 g 
C)  36 g 
D)  60 g 
E)  90 g 
A)  18 g 
B)  30 g 
C)  36 g 
D)  60 g 
E)  90 g

Question 19

The mobile shown in the figure is perfectly balanced, and the horizontal supports have insignificant masses. What must be the masses of the suspended objects m1, m2, and m3 to maintain balance?

Accepted Answer

m₁ = 1 g, m

Question 20

When a 125-kg piece of equipment is hung from a steel wire of length 75 cm, it stretches the wire by 4.00 mm. If instead the wire had a length of 150 cm, but all else were the same, by what distance would the same equipment stretch the wire?

Accepted Answer

A)  16.0 mm 
B)  8.00 mm 
C)  4.00 mm 
D)  2.00 mm 
E)  1.00 mm 
A)  16.0 mm 
B)  8.00 mm 
C)  4.00 mm 
D)  2.00 mm 
E)  1.00 mm

Exam 8: Equilibrium Ad Elasticity

Tensile strain is

A 1200-kg car is being raised with a constant acceleration of 2.53 m/s2 by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0 × 1011 N/m2. What is the change in length of the cable caused by lifting the car?

A uniform 1200-N piece of medical apparatus that is 3.5 m long is suspended horizontally by two vertical wires at its ends. A small but dense 550-N weight is placed on the apparatus 2.0 m from one end, as shown in the figure. What are the tensions, A and B, in the two wires?

A light board that is 10 m long is supported by two sawhorses, one at one end of the board and a second at the midpoint. A 40-N weight is placed between the two sawhorses, 3.0 m from the end and 2.0 m from the center. What magnitude forces do the sawhorses exert on the board?

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

A 1200-kg car is being raised at a constant speed if 25 cm/s by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0 × 1011 Pa. What is the change in length of the cable caused by the car?

An ornament of mass 40.0 g is attached to a vertical ideal spring with a force constant (spring constant) of 20.0 N/m. The ornament is then lowered very slowly until the spring stops stretching. How much does the spring stretch?

A 15-kg child is sitting on a playground teeter-totter, 1.5 m from the pivot. What is the magnitude of the minimum force, applied 0.30 m on the other side of the pivot, that is needed to make the child lift off the ground?

When a car is weighed, it is driven slowly on a horizontal floor over a scale that records a reading as the front wheels go over the scale, and then records a second reading as the rear wheels go over the scale. The weight of the car is equal to

A 10-m uniform beam weighing 100 N is supported by two vertical ropes at its ends. If a 400-N person sits at a point 2.0 m from the left end of the beam, what is the tension in each rope?

An irregularly shaped object that is 10 m long is placed with each end on a scale. If the scale on the right reads 96 N96 \mathrm {~N}96 N while the scale on the left reads 71 N, 71 \mathrm {~N} \text {, }71 N, how far from the left end is the center of gravity of this object?

A 50-kg bucket of concrete is suspended from a steel wire that is 1.0 mm in diameter 1.0 mm and 11.2 m long. What distance will the wire stretch? Young's modulus for steel is 2.0 x 1011 Pa.

An aluminum wire 2.0 m long and 2.0 mm in diameter supports a 10.0-kg fixture. What is the stress in the wire? Young's modulus for aluminum is 7.0 × 1010 N/m2.

A mobile is shown in the figure. The horizontal supports have negligible mass. Assume that all the numbers given in the figure are accurate to two significant figures. What mass M is required to balance the mobile?

The mobile shown in the figure is perfectly balanced, and the horizontal supports have insignificant masses. What must be the masses of the suspended objects m1, m2, and m3 to maintain balance?

When a 125-kg piece of equipment is hung from a steel wire of length 75 cm, it stretches the wire by 4.00 mm. If instead the wire had a length of 150 cm, but all else were the same, by what distance would the same equipment stretch the wire?

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A 1200-kg car is being raised with a constant acceleration of 2.53 m/s² by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0 × 10¹¹ N/m². What is the change in length of the cable caused by lifting the car?

A 1200-kg car is being raised at a constant speed if 25 cm/s by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0 × 10¹¹ Pa. What is the change in length of the cable caused by the car?

An irregularly shaped object that is 10 m long is placed with each end on a scale. If the scale on the right reads $96 \mathrm {~N}$ while the scale on the left reads $71 \mathrm {~N} \text {, }$ how far from the left end is the center of gravity of this object?

A 50-kg bucket of concrete is suspended from a steel wire that is 1.0 mm in diameter 1.0 mm and 11.2 m long. What distance will the wire stretch? Young's modulus for steel is 2.0 x 10¹¹ Pa.

An aluminum wire 2.0 m long and 2.0 mm in diameter supports a 10.0-kg fixture. What is the stress in the wire? Young's modulus for aluminum is 7.0 × 10¹⁰ N/m².

The mobile shown in the figure is perfectly balanced, and the horizontal supports have insignificant masses. What must be the masses of the suspended objects m₁, m₂, and m₃ to maintain balance?