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Engineering, section 1, Fall 2019
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Wickert & Lewis - Intro to Mech Engineering 4/e (Homework)

James Finch

Engineering, section 1, Fall 2019

Instructor: Dr. Friendly

Current Score : 34 / 38

Due : Sunday, January 27, 2030 12:00 EST

Last Saved : n/a Saving... ()

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Question

Points

1	2	3	4	5	6	7	8	9	10
2/2	2/3	2/3	9/9	7/7	1/1	1/2	2/3	4/4	4/4

Total

34/38 (89.5%)

Instructions

Introduce your students to the ever-changing field of mechanical engineering as you instill an appreciation for how engineers design hardware that builds and improves societies around the world. An Introduction to Mechanical Engineering, Enhanced Edition, by Jonathan Wickert and Kemper Lewis and published by Cengage Learning, is ideal for students in their first or second year of a college or university's mechanical engineering program. It is also useful for students in closely related fields. The authors balance the treatment of technical problem-solving skills, design, engineering analysis, and modern technology to provide the solid mechanical engineering foundation students need for future success.

Question 1 determines the components of a force during the power stroke of an internal-combustion engine.

Question 2 expresses the resultant of two kN forces acting on a rear tire in the directions perpendicular and parallel to a ramp as a vector using the unit vectors i and j, and determines the magnitude of the resultant and its angle relative to the incline.

Question 3 uses and compares the vector algebra and the vector polygon methods to determine the magnitude and direction of two forces and their resultant.

Question 4 gives an example of an Expanded Problem (EP). The question helps the student determine the moment of a force about the center of joint A by using the moment components method.

Question 5 is another example of an Expanded Problem (EP). The question helps the student find the magnitude and direction of the tension in the seat belt anchor strap during crash testing of an automobile where the lap and shoulder seat belt tensions are given.

Question 6 calculates the force that is being applied to a round metal bar held by adjustable pliers as a machinist grips its handles with P = 50 N.

Question 7 determines the cutting force F being applied to an steel pipe by a pair of large hydraulically operated shears.

Question 8 calculates the force acing at A of a multipurpose utility tool gripping a cotter pin at A while 15 lb. forces are applied to the handles. It also calculates what the force would be if the pin was being cut at B.

Question 9 determines the magnitudes and directions of the forces acting on the bearings supporting a shaft used to transmit power between two V-belts that apply forces of 1 kN and 1.4 kN to the shaft.

Question 10 determines the magnitude of the resultant force at the two supports, A and B, and the angle of each resultant force relative to the horizontal force exerted outward on the two supports of two pots of food being cooked on a solar cooker. This demo assignment allows many submissions and allows you to try another version of the same question for practice wherever the problem has randomized values.

Assignment Submission

For this assignment, you submit answers by question parts. The number of submissions remaining for each question part only changes if you submit or change the answer.

Assignment Scoring

Your last submission is used for your score.

1. 2/2 points | Previous Answers WLIntroMechEng4 4.2.003. My Notes

During the power stroke of an internal-combustion engine, the 480 lb pressure force pushes the piston down its cylinder (see figure).

A horizontal cylinder is closed at its right end with a piston going in its left side. In the gap between the piston and the right end of the cylinder, a force of 480 lb acts leftward. Rod A B goes up and left from A on the piston to a joint B above and left of A, where A B makes an angle of 14° with the horizontal. Another rod goes down and left from B to a crankshaft.

Determine the components of that force in the directions along and perpendicular to the connecting rod A B. (Enter the magnitudes in lb.)

force component along A B

466

lb force component perpendicular to A B

116

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2. 2/3 points | Previous Answers WLIntroMechEng4 4.3.005. My Notes

A hydraulic-lift truck carries a shipping container on the inclined loading ramp in a warehouse (see figure).

A construction vehicle is going up and left along a ramp inclined at 15° to the horizontal. A set of coordinate axes show that i points to the right and j points up. Two forces act at the rear tire.

A force of 17 kN points up and right perpendicular to the ramp.

A force of 2.9 kN points up and left parallel to the ramp.

The 17 kN and 2.9 kN forces act on a rear tire as shown in the directions perpendicular and parallel to the ramp.

(a)

Express the resultant of those two forces as a vector using the unit vectors i and j. (Let R be in kN. Do not include units in your answer.)

R =

1.60i+17.2j

$webMathematica generated answer key$ kN

(b)

Determine the magnitude of the resultant and its angle relative to the incline. (Enter the magnitude in kN and the angle in degrees counterclockwise from the plane of the incline.)

magnitude

17.2

kN angle

-80.3

° counterclockwise from the plane of the incline

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3. 2/3 points | Previous Answers WLIntroMechEng4 4.3.007. My Notes

The bucket of an excavator at a construction site is subjected to 1,300 lb and 620 lb digging forces at its tip (see figure).

An excavator vehicle has a large arm that goes up and left from its cab to a joint. Another arm goes down and left from the joint to end in a scoop bucket, where the scoop bucket would rotate counterclockwise about a pivot point to scoop material. A set of coordinate axes show that i points to the right and j points up. Two forces act at the tip of the bucket.

A force of 1,300 lb acts leftward.

A force of 620 lb acts up and left, making an angle of 50° with the leftward force.

Determine the magnitude and direction of their resultant. Use the vector algebra and the vector polygon methods. (Enter the magnitude in lb and the direction in degrees counterclockwise from i.)

magnitude

1760

lb direction

164

° counterclockwise from i

Compare the answers from the two methods to verify the accuracy of your work. (Submit a file with a maximum size of 1 MB.)

This answer has not been graded yet.

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4. 9/9 points | Previous Answers WLIntroMechEng4 4.4.015.EP. My Notes

Consider the industrial robotic arm shown below controlling a gripper C. The gripper is accidentally impacted by a 72 lb side load, directed perpendicular to BC. The lengths of the robot's links are

AB = 18 in.

and

BC = 12 in.

A robotic arm is composed of two segments that lie in the x y-coordinate plane, where the +x-axis is to the right and the +y-axis is up along the page.

Segment A B is oriented so that point A is fixed at the origin and point B is above and to the right of point A. A B makes an angle of 15° with the x-axis.

Segment B C goes up and right from point B to point C so that B C is rotated counterclockwise 40° from segment A B.

A 72 lb force acts up and left at point C, perpendicularly to segment B C.

What is the magnitude of the horizontal component of the 72 lb force (in lb)?

What is the magnitude of the vertical component of the 72 lb force (in lb)?

41.3

What is the total horizontal distance (in in.) between point A and point C?

24.3

in.

What is the total vertical distance (in in.) between point A and point C?

14.5

in.

What direction does the horizontal component of the 72 lb force want to turn the robotic arm around point A?

clockwise

counterclockwise

What direction does the vertical component of the 72 lb force want to turn the robotic arm around point A?

clockwise

counterclockwise

What is the cumulative moment (in in. · lb) created by the horizontal and vertical components of the 72 lb force around point A?

1860

in. · lb

If you convert this moment to ft · lb do you expect the magnitude to increase or decrease?

increase

decrease

Convert the moment to ft · lb.

155

ft · lb

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5. 7/7 points | Previous Answers WLIntroMechEng4 4.5.019.EP. My Notes

Consider the lap and shoulder automotive seat belts in the figures below. During a crash, the tension in each of those belts can be 249 lb.

The seat of a car and its seatbelt are viewed from the front. The seatbelt buckle, B, is at the bottom left corner of the seat. The lap belt extends rightward from B with a force of 249 lb to the right. The shoulder belt extends up and right from B at a 60° angle above the horizontal with a force of 249 lb acting up and right at the same angle. The third part of the belt goes down and left a short distance from buckle B to point A.

A seatbelt buckle is viewed from the front. An x y-coordinate plane shows the +x-axis going to the right and the +y-axis going upward. Three forces act on the buckle.

A force of 249 lb acts rightward.

A force of 249 lb acts up and right, 60° above the horizontal.

A force T acts down and left at acute angle θ below the horizontal.

What are the magnitudes of the horizontal and vertical components of the 249 lb force (in lb) that act across the lap portion of the seat belt?

T_x =

249

lb T_y =

What are the magnitudes of the horizontal and vertical components of the 249 lb force (in lb) that act diagonally over the shoulder?

T_x =

125

lb T_y =

216

What direction does the resultant anchor strap force act?

down and left down and right up and right up and left

What is the magnitude of the resultant anchor strap force? (in lb)

431

What is the angle (in degrees counterclockwise from the +x-axis) at which the anchor strap force acts?

-150

° counterclockwise from the +x-axis

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6. 1/1 points | Previous Answers WLIntroMechEng4 4.5.021. My Notes

Adjustable pliers hold a round metal bar as a machinist grips the handles with

P = 15 N

(see figure).

Two parts of a figure depict a set of adjustable pliers gripping a round metal bar. The bar A extends into the page. The upper jaw starts at the top of the bar, goes up and right, turns at a right angle, goes down and right to joint B, continues down and right in the same direction, then goes directly to the right to the end of the lower handle at D. The upper jaw starts at the bottom of the bar, goes to the right and slightly upward to joint B, and continues directly to the right to the end of the upper handle at C. The joint B linking the two handles is directly to the right of the bar.

In the first figure part, a force P acts downward on the upper handle at C, and another force acts upward on the lower handle at D. The distance from the bar to joint B, in a direction perpendicular to the line between the center of the bar and the point of contact between the bar and lower jaw, is 20 mm. The distance from the end of the upper handle to joint B, in a direction perpendicular to the force P on the upper handle, is 130 mm.

The second figure part focuses on the lower jaw and upper handle. The force by the pipe on the lower jaw is also labeled A, and acts down and to the right on the lower jaw, perpendicular to the tangent along the pipe's circumference where the pipe contacts the lower jaw. Coordinate axes are drawn at joint B, with the +B_x-axis to the right and the +B_y-axis upward. Force P acts downward on the right end of the upper handle.

Using the free body diagram shown for the combined lower jaw and upper handle, calculate the force A that is being applied to the bar. (Enter the magnitude in N.)

97.5

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7. 1/2 points | Previous Answers WLIntroMechEng4 4.5.023. My Notes

A pair of large hydraulically operated shears in the figure below is attached to the end of the boom on an excavator.

Two parts of a figure show a pair of hydraulically operated shears attached to a boom. The shears make contact about and apply a force to a hollow cylindrical pipe.

In the first figure part, key points are labeled. The upper jaw starts at the top of the pipe and goes to the right and slightly upward to point A, where the jaw connects to a hydraulic cylinder A B. The lower jaw starts at the bottom of the pipe and goes to the right to point B at the other end of the cylinder. The cylinder goes down and right from A to B. The jaws connect at joint C, a short distance to the right of the center of the pipe. The boom connects to the bottom of the lower jaw and extends down and to the right.

In the second figure part, physical properties are given.

The hydraulic cylinder applies a force on the upper jaw equal to 19 kN, oriented up and to the right, along the axis of the cylinder. The distance from joint C to the cylinder, in a direction perpendicular to this force, is 1.7 m.

The lower jaw applies a force F on the pipe, oriented up and to the left, perpendicular to the tangent of the pipe's circumference along which the lower jaw lies. The distance from the pipe to joint C, in a direction perpendicular to this force, is 1.2 m.

The shear is used for cutting steel pipe and I-beams during demolition work. Hydraulic cylinder AB exerts a 19 kN force on the upper jaw.

(a)

Complete the free body diagram for the upper jaw, which has been only partially drawn. (Submit a file with a maximum size of 1 MB.)

This answer has not been graded yet.

(b)

Determine the cutting force F being applied to the pipe. (Enter the magnitude in kN.)

26.9

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8. 2/3 points | Previous Answers WLIntroMechEng4 4.5.027. My Notes

A multipurpose utility tool grips a cotter pin at A while 10.5 lb forces are applied to the handles (see figure).

A horizontal utility tool similar to a pair of pliers grips a cotter pin. The tool is oriented with the handles on the right. The pin is held in the jaws at point A. The two halves of the jaw meet as a pair of blades at point B to the right of point A. The joint that connects the two halves of the tool is at point C, 1⁄2 in. to the right of point B and 1 1⁄4 in. to the right of point A. A force of 10.5 lb is applied to each handle at point D, a horizontal distance of 4 1⁄2 in. to the right of point C. The top handle experiences a downwards force and the bottom handle experiences an upwards force.

A second figure shows a partial free body diagram that highlights the half of the tool that makes up the top jaw and the bottom handle. The bottom handle experiences the upwards 10.5 lb force.

(a)

Complete the free body diagram of the combined upper jaw and lower handle assembly, which has been only partially drawn. (Submit a file with a maximum size of 1 MB.)

This answer has not been graded yet.

(b)

Calculate the force acting at A. (Enter the magnitude in lb.)

37.8

(c)

Alternatively, what would the force be if the pin was being cut at B? (Enter the magnitude in lb.)

94.5

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9. 4/4 points | Previous Answers WLIntroMechEng4 4.3.030. My Notes

Ball bearings support a shaft at points A and B (see figure).

A horizontal shaft of length 18 cm is supported at its left end A and its right end B. Two vertical belts make contact with and apply a force to the horizontal shaft.

One belt is a distance 6 cm to the right of A, and applies an upward force of 4.0 kN on the shaft.

The other belt is a distance 6 cm to the left of B, and applies a downward force of 7.0 kN on the shaft.

The shaft is used to transmit power between two V-belts that apply forces of 4.0 kN and 7.0 kN to the shaft. Determine the magnitudes (in kN) and directions of the forces acting on the bearings. (Due to the nature of this problem, do not use rounded intermediate values in your calculations—including answers submitted in WebAssign.)

Force at A:

magnitude

0.333

kN direction

downward

Force at B:

magnitude

3.33

kN direction

upward

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10. 4/4 points | Previous Answers WLIntroMechEng4 4.3.032. My Notes

Two pots of food are being cooked on a solar cooker (see figure).

A solar cooker is comprised of a parabolic reflector with a horizontal bar A B of 30 in. length going through the reflector at either end of its diameter. The bar is connected to a fixed frame that supports the system. The bar supports a smaller pot 14 in. to the right of A and a larger pot 18 in. to the right of A.

The smaller pot weighs 2 lb, and the larger pot weighs 7 lb. Also, due to the thermal expansion of the parabolic reflector, a horizontal force of 0.49 lb is exerted outward on the two supports. Determine the magnitude of the resultant force (in lb) at the two supports, A and B, and the acute angle (in degrees) of each resultant force relative to horizontal.

A =

3.9

lb B =

5.16

θ_A

82.8

θ_B

84.5

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Wickert & Lewis - Intro to Mech Engineering 4/e (Homework)

Current Score : 34 / 38

Due : Sunday, January 27, 2030 12:00 EST

Last Saved : n/a Saving... ()

Instructions

Assignment Submission

Assignment Scoring