Question 1

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

Accepted Answer

A) True 
 B)False

Question 2

There must be equal amounts of mass on both sides of the center of mass of a system.

Accepted Answer

A) True 
 B)False

Question 3

An object of 3.0-kg mass is located at (0.0 m,8.0 m),and an object of 1.0-kg mass is located at (12 m,0.0 m).You want to add a 4.0-kg object so that the center of mass of the three-object system will be at the origin.What should be the coordinates of the 4.0-kg object?

Accepted Answer

A) (-3.0 m, -6.0 m) 
B) (-12 m, -8.0 m) 
C) (3.0 m, 6.0 m) 
D) (-6.0 m, -3.0 m) 
A) (-3.0 m, -6.0 m) 
B) (-12 m, -8.0 m) 
C) (3.0 m, 6.0 m) 
D) (-6.0 m, -3.0 m)

Question 4

Three small objects are positioned at the following coordinates: the 3-0 kg object at (3.0 m,2.0 m); the 4.0-kg object at (0.0 m,-1.0 m); and the 5.0-kg object at (5.0 m,-7.0 m).What are the coordinates of the center of mass of this system?

Accepted Answer

The answer of Three small objects are positioned at the...

Question 5

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 mass 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 6

Two equal-magnitude forces are exerted to a door at the doorknob.The first force is exerted perpendicular to the door,and the second force is exerted at 30° to the plane of the door.Which force exerts the greater torque about the door hinge?

Accepted Answer

A) the first force (exerted perpendicular to the door) 
B) the second force (exerted at an angle) 
C) Both forces exert equal non-zero torques. 
D) Both forces exert zero torque. 
A) the first force (exerted perpendicular to the door) 
B) the second force (exerted at an angle) 
C) Both forces exert equal non-zero torques. 
D) Both forces exert zero torque.

Question 7

The lug nuts on a car wheel require tightening to a torque of 90 N ∙ m.If a 30-cm long wrench is used,what is the magnitude of the minimum force required using the wrench?

Accepted Answer

A) 300 N 
B) 150 N 
C) 30 N 
D) 15 N 
A) 300 N 
B) 150 N 
C) 30 N 
D) 15 N

Question 8

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 9

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 10

An 82-kg diver stands at the edge of a light 5.0-m diving board,which is supported by two vertical pillars that are 1.6 m apart,as shown in the figure.Find the magnitude and direction of the force exerted by each pillar.

Accepted Answer

A: 1.7 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 object 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 m...

Question 12

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,15-N object,is placed on the supported end.What magnitude forces do the sawhorses exert on the board?

Accepted Answer

1.0 N at t

Question 13

As shown in the figure,a given force is applied to a rod in several different ways.In which case is the torque about the pivot P due to this force the greatest? $1 .$
 
$2 .$
  
$3 .$
 
$4 .$
 
$5 .$

Accepted Answer

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

Question 14

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 force that the cable connected between points B and D exerts on the boom?

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 15

A 40-kg uniform ladder that is 5.0 m long is placed against a smooth wall at a height of h = 4.0 m,as shown in the figure.The base of the ladder rests on a rough horizontal surface whose coefficient of static friction with the ladder is 0.40.An 80-kg bucket is suspended from the top rung of the ladder,just at the wall.What is the magnitude of the force that the ladder exerts on the wall?

Accepted Answer

A) 740 N 
B) 1300 N 
C) 980 N 
D) 900 N 
E) 1100 N 
A) 740 N 
B) 1300 N 
C) 980 N 
D) 900 N 
E) 1100 N

Question 16

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 force that the wire exerts on the sign?

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 17

A uniform ladder 12 meters long rests against a vertical frictionless wall,as shown in the figure.The ladder weighs 400 N and makes an angle θ = 51° with the floor.A man weighing 874 N climbs slowly up the ladder.When he is 78 m from the bottom of the ladder,it just starts to slip.What is the coefficient of static friction between the floor and the ladder?

Accepted Answer

The answer of A uniform ladder 12 meters long rests...

Question 18

To determine the location of the center of mass 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 19

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 reading of the scale when it is under the front wheels. 
B) the reading of the scale when it is under the rear wheels. 
C) the average of the two readings. 
D) the sum of the two readings . 
E) the difference of the two readings. 
A) the reading of the scale when it is under the front wheels. 
B) the reading of the scale when it is under the rear wheels. 
C) the average of the two readings. 
D) the sum of the two readings . 
E) the difference of the two readings.

Exam 8: Extended Bodies at Rest

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

There must be equal amounts of mass on both sides of the center of mass of a system.

An object of 3.0-kg mass is located at (0.0 m,8.0 m),and an object of 1.0-kg mass is located at (12 m,0.0 m).You want to add a 4.0-kg object so that the center of mass of the three-object system will be at the origin.What should be the coordinates of the 4.0-kg object?

Three small objects are positioned at the following coordinates: the 3-0 kg object at (3.0 m,2.0 m); the 4.0-kg object at (0.0 m,-1.0 m); and the 5.0-kg object at (5.0 m,-7.0 m).What are the coordinates of the center of mass of this system?

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 mass of this object?

Two equal-magnitude forces are exerted to a door at the doorknob.The first force is exerted perpendicular to the door,and the second force is exerted at 30° to the plane of the door.Which force exerts the greater torque about the door hinge?

The lug nuts on a car wheel require tightening to a torque of 90 N ∙ m.If a 30-cm long wrench is used,what is the magnitude of the minimum force required using the wrench?

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 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?

An 82-kg diver stands at the edge of a light 5.0-m diving board,which is supported by two vertical pillars that are 1.6 m apart,as shown in the figure.Find the magnitude and direction of the force exerted by each pillar.

As shown in the figure,a given force is applied to a rod in several different ways.In which case is the torque about the pivot P due to this force the greatest? 1.1 .1. 2.2 .2. 3.3 .3. 4.4 .4. 5.5 .5.

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

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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 mass of this object?

As shown in the figure,a given force is applied to a rod in several different ways.In which case is the torque about the pivot P due to this force the greatest? $1 .$ $2 .$ $3 .$ $4 .$ $5 .$