ASSIGNMENT 1

Textbook Assignment: “Levers,” chapter 1, pages 1-1 through 1–8; Block and Tackle,” chapter2, pages 2–1 through 2--6; “The Wheel and Axle,” chapter 3, pages 3–1through 3–6; “The Inclined Plane and the Wedge,” chapter 4, pages: 4–1through 4–2.

1-1. A chain hoist lifts a 300–poundload through a height of 10 feetbecause it enables you to lift theload by exerting less than 300pounds of force over a distance of10 feet or less.

1. True2. False

1–2. When a chain hoist is used tomultiply the force being exerted ona load, the chain is pulled at afaster rate than the load travels.

1. True2. False

1–3. What are the six basic simplemachines?

1.

2.

3.

4.

The lever, the block andtackle, the inclined plane, theengine, the wheel and axle, andthe gearThe lever, the block andtackle, the wheel and axle, thescrew, the gear, and theeccentricThe lever, the block andtackle, the wheel and axle, theinclined plane, the screw, andthe gearThe lever, the inclined plane,the gear, the screw, thefulcrum, and the torque

1–4. Which of the following basicprinciples is recognized byphysicists as governing each simplemachine?

1. The wedge or the screw2. The wheel and axle or the gear3. The lever or the inclined plane4. The block and tackle or the

wheel and axle

1–5. Which of the following simplemachines works on the sameprinciple as the inclined plane?

1. Screw2. Gear3. Wheel and axle4. Block and tackle

1-6. The fundamentally important pointsin any lever problem are (1) thepoint at which the force isapplied, (2) the fulcrum, and (3)the point at which the

1. lever will balance2. resistance arm equals the

effort arm3. mechanical advantage begins to

increase4. resistance is applied

1

1–11. You will find it advantageous touse a third-class lever when thedesired result is

1. a transformation of energy2. an increase in speed3. a decrease in applied effort4. a decrease in speed and an

increase in applied effort

1–7. Which, if any, of the followingparts illustrates a first classlever?

1. A2. B or C3. D4. None of the above

1–8. Which part illustrates asecond–class lever?

1. D2. C3. B4. A

1–9. What part illustrates a third–classlever?

1. A2. B3. C4. D

1–10. Which of the following classes oflevers should you use to lift alarge weight by exerting the leasteffort?

IN ANSWERING QUESTIONS 1-12 THROUGH

o 1–14, SELECT THE CORRECT ARMMEASUREMENTS FROM FIGURES 1B AND 1C.

1–12. Effort arm in figure 1B

1. 1 ft2. 3 ft3. 4 ft4. 5 ft

1–13. Resistance arm in figure 1B

1. 1 ft2. 3 ft3. 4 ft4. 5 ft

1–14. Resistance arm in figure 1C

1. 1 ft2. 3 ft3. 4 ft4. 5 ft

1. First–class2. Second–class3. First– or second–class4. Third–class

2

1–15. Two boys find that they can balanceeach other on a plank if one sitssix feet from the fulcrum and theother eight feet. The heavier boyweighs 120 pounds. How much doesthe lighter boy weigh?

1. 90 lb2. 106 lb3. 112 lb4. 114 lb

1–16. With the aid ofshown in figure

the1D,

pipe wrenchhow many pounds

of effort will you need to exert toovercome a resistance of 900pounds?

1. 25 lb2. 50 lb3. 75 lb4. 100 lb

Questions 1-17 and 1–18 are relatedo to a 300–pound load of firebrick

stacked on a wheelbarrow. Assume that theweight of the firebrick is centered at apoint and the barrow axle is 1 1/2 feetforward of the point.

1–17.

1-18.

1-19.

If a Seaman grips the barrowhandles at a distance of three feetfrom the point, how many totalpounds will the Seaman have to liftto move the barrow?

1. 65 lb2. 100 lb3. 150 lb4. 300 lb

If a Seaman grasps the handles3 1/2 feet from the point where theweight is centered, how many poundsof effort will be exerted?

1. 50 lb2. 90 lb3. 100 lb4. 120 lb

In lever problems, the length ofthe effort arm multiplied by theeffort is equal to the length ofthe

1. resistance arm multiplied bythe effort

2. resistance arm multiplied bythe resistance

3. effort arm multiplied by theresistance arm

4. effort arm multiplied by theresistance

1-20. The length of the effort arm infigure 1E is equal to the length ofthe

1. curved line from A to C2. curved line from A to D3. straight line from B to C4. straight line from B to D

3

1–21. Refer to figure 1F. If a personexerts at point B a pull of 60pounds on the claw hammer shown,what is the resistance that thenail offers?

1. 60 lb2. 120 lb3. 480 lb4. 730 lb

1–22. Which of the following definitionsdescribes the mechanical advantageof

1.

2.

3.

4.

the lever?

Effort that must be applied toovercome the resistance of anobject divided by theresistance of the objectAmount of work obtained fromthe effort appliedGain in power obtained by theuse of the leverResistance offered by an objectdivided by the effort whichmust be applied to overcomethis resistance

1–23. The mechanical advantage of leverscan be determined by dividing thelength of the effort arm by the

1. distance between the load andthe point where effort isapplied

2. distance between the fulcrumand the point where effort isapplied

3. distance between the load andthe fulcrum

4. amount of resistance offered bythe object

1–24. The mechanical advantage of thelever in figure 1G is

1. one–fifth2. one-fourth3. four4. five

1–25. The mechanical advantage of thelever in figure 1H is

1. one2. two3. one–half4. one–fourth

4

1-30. The rope in a block and tackle iscalled a

1–26. The mechanical advantage of thelever pictured in figure 1J is

1. five2. six3. seven4. one–sixth

1–27. The combination dog and wedge oftextbook figure 1-10 is a complexmachine since it consists of whichtwo simple machines?

1. Lever and the screw2. Two first–class levers3. Lever and the inclined plane4. One first-class lever and one

second-class lever

Information for questions 1-28 and

$ 1-29: The handle of a hatch dog is9 inches long. The short arm is 3 incheslong.

1-28. What is the mechanical advantage ofthe hatch dog?

1. 122. 273. 34. 9

1–29. With how much force must you pushdown on the handle to exert 210pounds force on the end of theshort arm?

1. 105 lb2. 80 lb3. 70 lb4. 25 lb

1. runner2. line3. fall4. sheave

1-31. The theoretical mechanicaladvantage of the single sheaveblock of textbook figure 2-2 is

1. one2. two3. one-half4. zero

1-32. A single block-and-fall rigged as arunner has a theoretical mechanicaladvantage of

1. one2. two3. one–half4. four

1-33. In a block and tackle having amechanical advantage greater thanone, how does the distance the loadmoves compare with the length ofthe rope which is pulled throughthe block?

1. It is less2. It is the same3. It is greater4. It depends on the weight of the

load

1-34. What advantage can you obtain byreplacing the single fixed block oftextbook figure 2-3 with the guntackle purchase of textbook figure2-6?

1. You can pull the rope from amore convenient position

2. You need to exert about 1/3 asmuch effort to lift the sameload

3. You can lift the same load in1/2 the time

4. You need to exert about 1/2 asmuch effort to lift the sameload

5

1-35. In the arrangement of figure 1K thepurpose of block A is to

1. increase the mechanicaladvantage of the block

2. change the direction of theapplied force

3. hold up block B4. act as a runner for block B

1–36. A luff tackle is a block and tackleconsisting of a

1-38. For which requirement will it be toyour advantage to rig a yard to astay tackle if each tackle has atheoretical mechanical advantage oftwo?

1. A theoretical mechanicaladvantage of 4

2. A change in the direction ofpull for convenience

3. A heavy crate to be lifted tothe other side of a low fence

4. An increase in speed

1. fixed double block and amovable single block

2. movable double block and afixed single block

3. fixed single block and amovable single block

4. fixed triple block and a 1–39. The overall mechanical advantage inmovable double block figure 1L is about

Information for questions 1-37 and

o 1–38: Alone you’re going to hoista 600–pound load to a height of 36 feet.You can pull 160 pounds’ worth. You haveto use a fixed block fastened to a beamabove you. You have a movable blockattached to the pad eye of the load.

1–37. What minimum mechanical advantagemust the block and tackle provide?

1. One2. Two3. Three4. Four

1. five2. six3. eight4. twelve

1-40. You are using a differential pulleyto lift a load of 2,400 pounds.Fifty pounds of effort are requiredto overcome the frictionalresistance of the pulley. Whatforce is necessary to lift the loadif the theoretical mechanicaladvantage of the pulley is 24?

1. 50 lb2. 100 lb3. 150 lb4. 200 lb

6

1–41. With a block and tackle the efforthas to move 125 feet in order toraise a load 25 feet. The frictionis so great that it takes a forceof 75 pounds to lift a load of 300pounds. The actual mechanicaladvantage is

1. five2. two3. three4. four

1-42. The theoretical mechanicaladvantage of a differential pulley,such as the one pictured in figure1M, depends upon the

1. difference in diameters of thetwo top pulleys

2. sum of diameters of the two toppulleys

3. length of the chain4. difference in diameters of the

two small pulleys

1-43. In the differential pulley picturedin figure 1M, if the radius of thesmall pulley at the top is 3inches, the radius of the largepulley at the top is 4 inches, andthe radius of the pulley at thebottom is 2 1/2 inches, thetheoretical mechanical advantage is

1. 82. 93. 304. 36

1-44. Why is the actual mechanicaladvantage of the differentialpulley of textbook figure 2–11never so great as the theoreticalmechanical advantage of the pulley?

1. Part of the effort applied tothe chain is used to overcomethe frictional resistance ofthe pulley’s moving parts

2. The diameter of C is betweenthose of A and B

3. The diameter of A is greaterthan that of B

4. The length of the chain feddown is greater than the lengthof the chain fed up

1-45. A wheel and axle can rotateclockwise or counterclockwise aboutan axis to provide a mechanicaladvantage or an increase in speed.

1. True2. False

1-46. The mechanical advantage of a wheeland axle depends upon the

1. amount of force applied and thesize of the wheel

2. size of the wheel and theamount of the resistance

3. ratio of the radius of thewheel to which force is appliedto the radius of the axle onwhich it turns

4. length of the axle

7

1-47. What maximum load can you lift byapplying a 50–pound force to thehandle of an 18–inch crank that isconnected to a 9–inch-diameter drumof a hand winch?

1. 50 lb2. 100 lb3. 150 lb4. 200 lb

1–48. The moment resulting from a forceacting on a wheel and axle is equalto the

1.

2.

3.

4.

amount of force required toproduce equilibrium in a wheeland axleratio of the force to thedistance from the center ofrotationdistance from the point wherethe force is applied to thecenter of the axleproduct of the amount of theforce and the distance of theforce from the center ofrotation

1-49. The clockwise moment of force aboutthe fulcrum of figure 1N is

1. 4 2/3 ft-lb2. 6 ft-lb3. 25 ft-lb4. 150 ft-lb

1-50. If in the lever shown in figure 1Nboth the amount of force and thedistance between the fulcrum andthe point where force is appliedare doubled, the torque will be

1. 1/2 as great as before thechanges were made

2. 2 times as great as before thechanges were made

3. 4 times as great as before thechanges were made

4. 8 times as great as before thechanges were made

1-51. What would be the resultant torquein figure 1P?

1. Clockwise torque of 10 ft–lb2. Clockwise torque of 14 ft-lb3. Counterclockwise torque of 10

ft-lb4. Counterclockwise torque of 14

ft-lb

1-52. What will happen to a machine whenclockwise and counterclockwisemoments of force are in balance?

1. The machine will break down2. The machine will either remain

at rest or move at a steadyspeed

3. The machine will move at anincreasing speed

4. The machine will move at adecreasing speed

8

1–53. The result of forces acting asshown in figure 1Q would be atorque of

1. 600 ft-lb2. 1,180 ft–lb3. 1,820 ft–lb4. 2,680 ft–lb

Information to answer questions

o 1–54 through 1-56: The servicemanual for an engine states that a certainnut is to be tightened by a moment of 90foot–pounds.

1–54.

1-55.

1–56.

If a wrench 18 inches long is used,the amount of force that should beexerted at the end of the wrench is

1. 5 lb2. 9 lb3. 60 lb4. 162 lb

How many pounds of effort could besaved by using a two-foot longwrench?

1. 15 lb2. 30 lb3. 45 lb4. 50 lb

What kind of wrench could you usethat measures directly the amountof force you are exerting on thenut?

1. Pipe wrench2. Torque wrench3. Spanner wrench4. Adjustable end wrench

1–57. The result of forces operating asshown in figure 1R is equivalent toa moment of

1. 300 ft–lb in a clockwisedirection

2. 700 ft-lb in a counterclockwisedirection

3. 4,500 ft-lb in a clockwisedirection

4. 6,000 ft–lb in acounterclockwise direction

When answering questions 1–58

o through 1-60, refer to figure 1S.

1–58. The clockwise moment about A is

1. 200 ft–lb2. 300 ft-lb3. 1,200 ft–lb4. 1,800 ft–lb

9

1–59.

1–60.

1–61.

1-62.

The counterclockwise moment about Bis

1. 200 ft–lb2. 1,200 ft–lb3. 1,800 ft–lb4. 3,000 ft–lb

How much of the load is the sailorat the right carrying?

1. 22 2/9 lb2. 33 1/3 lb3. 80 lb4. 120 lb

The sailor in figure 3-4 in yourtextbook can increase hiseffectiveness without exerting agreater effort by using a shortercapstan bar.

1. True2. False

Which of the parts of figure 1Trepresents the wheel and axlearrangement known as a couple?

1. A2. B3. C

1–63.

1-64.

0

A ship’s deck is 24 feet above thedock. How long a gangplank isneeded to provide a theoreticalmechanical advantage of 2?

1. 24 ft2. 48 ft3. 60 ft4. 96 ft

A sailor is rolling a 400–poundbarrel up a 20–foot long ramp to a3-foot height. Neglectingfriction, the force needed to movethe barrel up the ramp is

1. 60 lb2. 133 1/3 lb3. 200 lb4. 220 lb

When answering questions 1–65through 1-68, refer to figure 1U.

1–65. The theoretical mechanicaladvantage of the inclined plane is

1. 3/162. 33. 5 1/34. 6

1-66. Neglecting friction, the force,needed to pull the crate up theinclined plane is

1. 50 lb2. 75 lb3. 124 lb4. 600 lb

4. D

10

1–67.

1–68.

1-69.

0

If a force of 133 pounds isactually required to move the crateup the inclined plane, the amountof force expended in overcomingfriction is

1. 20 lb2. 33 lb3. 58 lb4. 66 lb

Since a force of 133 pounds wasexerted in moving the crate up theinclined plane, the actualmechanical advantage is

1. 1/32. 2 1/33. 34. 4

A 3,000–pound automobile is towedup a ramp 150 feet long runningfrom the street floor to the secondfloor of a garage. The towingforce required was 300 pounds.What is the distance between floorsif 20 pounds of force were neededto overcome frictional resistance?

1. 8.6 ft2. 10 ft3. 14 ft4. 15 ft

Information for questions 1–70 and1–71: By exerting an effort of 115

pounds, you move a 300–pound crate up aninclined plane 12 feet long to a truck bedthree feet above the sidewalk.

1–70. What is the theoretical mechanicaladvantage of the inclined plane?

1. One2. Two3. Three4. Four

1–71. How much of your effort is used toovercome friction?

1. 35 lb2. 40 lb3. 75 lb4. 115 lb

1–72. What is the characteristic shape ofwedges which have a high mechanicaladvantage?

1. Short and thick2. Long and thin3. Long and thick4. Short and thin

1–73. If a wedge is 6 inches long, 3inches wide, and 1 1/2 inches thickat the top, the theoreticalmechanical advantage is

1. 1 1/22. 23. 34. 4

1–74. A member of a damage control partyuses a maul to drive a wedge inbehind a shore to tighten up adamaged bulkhead. The wedge is 15inches long and 3 inches thick atthe butt. How many pounds of forcewill be delivered against the faceof the wedge by an 80–pound blow onthe wedge butt with the maul?

1. 80 lb2. 240 lb3. 400 lb4. 1,200 lb

1-75. A 60–pound blow delivered againstthe 3/4–inch–thick butt end of awedge results in an effectivesplitting force of 480 pounds. Howlong is the wedge?

1. 3 in2. 4 in3. 6 in4. 8 in

11