Work And Machines ANSWER KEY - Lab35

ANSWER KEYWork and MachinesChapter ProjectWorksheet 11. inclined plane, wedge, screw, lever, wheelWhat Is Work?Guided Reading and StudyUse Target Reading SkillsSample questions and answers:Q. What is work?A. Work is done when a force causes an object tomove in the direction of the force.Q. How is work calculated?A. Work is force times distance.Q. What is power?A. Power is the rate at which work is done.1. You do work when you exert a force on anobject that causes the object to move a distancein the same direction as the exerted force.2. pull out books: worklift newspapers: workpush on stuck car: no workhold wood in place: no workpull sled: workhold bag: no work3. distance4. In carrying an object, you exert an upwardforce. But to do work, you must exert a force inthe same direction as the object’s motion. Sincethe object’s motion is horizontal and the forceextended is vertical, no work is done.5. When you pull a suitcase with wheels, youpull at an angle to the ground. Your force has ahorizontal part and a vertical part. Only the horizontal part does work because that force is inthe same direction as the motion of the suitcase.force, distancetrueWork Force Distancejoule, or N·m1 joulePower is the rate at which work is done orthe amount of work done in a unit of time.12. true13. Power Work Time14. Power (Force Distance) TimeWhat Is Work?Review and Reinforce1. She is doing work if the force causes thebox to move some distance in the direction ofthe force.2. Use this formula: Work Force Distance3. 80 J4. Exerting a force on an object that causes theobject to move some distance in the direction ofthe force.5. Amount of work done when you exert aforce of 1 newton to move an object a distance of1 meter.6. The rate at which work is done.What Is Work?EnrichTotal Work (in joules)5043.535.52501. As the angle increases, the fraction of theforce that contributes to work decreases.2. None of the force applied to the object contributed to its movement because the directionsof the force and movement were at right anglesto one another.3. No Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.Work and Machinesand axle, pulley2. pulley3. lever4. inclined plane5. Answers will vary: top, side, or bottom6. Answers will vary; only one of the six simple machines must be mentioned.7. Answers will vary; only one of the six simple machines must be mentioned.8–10. Students’ designs will vary.6.7.8.9.10.11.

ANSWER KEYWork and MachinesHow Machines Do WorkGuided Reading and StudyUse Target Reading SkillsSample main idea: The mechanical advantage ofa machine helps by:Sample details:changing forcechanging distancechanging direction1. A machine is a device with which you cando work in a way that is easier or more effective.2. false3. a, c, d4. input force5. output force6. true7. distance8. true9.Input forceOutput forceHow Machines Do WorkReview and Reinforce1. true2. increasing3. true4. without5. mechanical advantage6. input force7. machine8. ideal mechanical advantage9. actual mechanical advantage10. efficiency11. output forceHow Machines Do WorkEnrich1. The person is pulled downward by theforce of gravity.2. Force 75 kg 9.8 m/s2 735 NWork 735 N 0.5 m 367.5 J3. Force 750 kg 9.8m/s2 7,350 NWork 7,350 N 0.05m 367.5 JIt is the same amount of work.4. Input force: 735 NOutput force: 7,350 NMechanical advantage: 7,350 N 735 N 105. Efficiency: (367.5 J 367.5 J) 100% 100%.This is complete efficiency and is very unlikely.Friction would cause a real treadmill to be lessefficient.Seesaw ScienceSkills LabFor answers, see the Teacher’s Edition.10. The number of times a force exerted on amachine is multiplied by the machine.11. Mechanical advantage Output force Input force12. output, input13. friction14. efficiency15. Efficiency (Output work Input work) 100%16. actual17. ideal Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.

ANSWER KEYWork and Machines16. Second-class leverSimple MachinesGuided Reading and Study1. inclined plane, lever, wedge, wheel andaxle, screw, pulley2. An inclined plane is a flat, slanted surface.3. Ideal mechanical advantage length ofincline height of incline4. a, b, d5. input force6. A wedge is a device that is thick at one endand tapers to a thin edge at the other end.7. true8. true9. A screw is an inclined plane wrappedaround a cylinder.10. threads11. The input force is applied to the top of thescrew. As the screw turns, the threads exert anoutput force on the wood.12. A lever is a rigid bar that is free to pivot, orrotate, around a fixed point.13. fulcrum14. a, b, c26.15.First-class umSecond-class leversInputforceOutputforceFulcrumThird-class leversInputforceInputforceFulcrum Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.OutputforceWork and MachinesUse Target Reading SkillsSample questions and answers:Q. What are the three classes of levers?A. First, second, and thirdQ. Which type of lever always changes thedirection of the input force?A. First-class leversFirst-class leverThird-class lever17. Ideal mechanical advantage distancefrom fulcrum to input force distance from fulcrum to output force18. A wheel and axle is a simple machine madeof two circular objects that are fastened togetherand that rotate around a common axis.19. Ideal mechanical advantage Radius ofwheel Radius of axle20. A pulley is a grooved wheel with a rope (orchain, or even a steel cable) wrapped around it.21. fixed pulley22. moveable pulley23. They consist of bones and muscles.24. tendons25. The joint near where the tendon is attachedto the bone acts as the fulcrum.

ANSWER KEYWork and Machines27. wedges28. When you bite down on something, thewedge shape of your teeth produces enoughforce to break it in half, just as an ax is used tosplit a log.29. A compound machine is a machine thatutilizes two or more simple machines.30. You must know the mechanical advantageof each simple machine utilized in the compound machine.Simple MachinesReview and Reinforce1. wedge2. wheel and axle3. lever4. inclined plane5. pulley6. screw7. compound machine8. lever9. pulley10. screw11. inclined plane12. fulcrum13. wedge14. wheel and axleSimple MachinesEnrich1. lever2. inclined plane3. pulley4. wheel and axle5. first-class lever6. the magnifying glass (A) and theAngling for AccessSkills LabFor answers, see the Teacher’s Edition.Key Terms1. wedge2. compound3. output4. fulcrum5. work6. axle7. efficiency8. lever9. input10. inclined11. pulley12. machine13. joule14. screwMath Skills1. 350 J2. 15,000 J3. 25,000 W or 25 kW4. 200 W5. 46. 37. 50%8. 75%9. 410. 511. 212. 213. 1214. 6paper bag (B) Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.

Forcemultiplied byDistancemeasuredusing the unitJouleequalsPowermeasuredusing the unitWattisTimedivided byCompoundmachinescombineto formSimplewhichcan besixtypesMachinesmade easier by Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.whichis anwhichis anWedgeScrewwhichiswhichiswhichis awhichis aPulleyWheeland dsurfaceDirectionDistanceForcewrappedaround athatcanaroundathatrotatearound anwhichpivotsaround aCylinderMoveGroovedwheelAxisFulcrumThis concept map is only one way to representthe main ideas and relationships in thisWork and MachinesWorkWork and MachinesANSWER KEYConnecting Conceptschapter. Accept other logical answers fromstudents.

ANSWER KEYWork and MachinesLaboratory InvestigationMore to ExplorePulleys as Simple MachinesIf the input force and the output force move thesame distance, the pulley system will have amechanical advantage of 1. If the input forcemoves a greater distance than the output forcemoves, the pulley will have a mechanicaladvantage greater than 1.Pre-Lab Discussion1. The mechanical advantage of a machine isthe number of times a machine multiplies aforce exerted on it.2. Machines make work easier by changingthe direction or amount of force needed toaccomplish a task. Pulleys and pulley systemsdo both of these.Analyze and Conclude1. Yes, The single fixed pulley has an idealmechanical advantage of 1; the ideal mechanicaladvantage of the single moveable pulley is 2.Actual mechanical advantage for these pulleyswill probably be somewhat different because offriction and measurement of error.2. Less input force was needed with morepulleys.3. The number and arrangement of the pulleys determine what the mechanical advantagewill be.Critical Thinking and Applications1. The single fixed pulley has an idealmechanical advantage of 1. Its practical use is tochange the direction of effort.2. a. 1b. 2c. 2d. 3e. 43. Mechanical advantage for a pulley systemis the same no matter how it is calculated. However, measurements of actual mechanicaladvantages will vary because of friction andmeasurement error.4. Diagrams should show six supporting sections of rope.5. The distance through which the input forcemoves increases.6. In a machine, work output can never begreater than work input. Because work input isinput force times distance, if the input forcedecreases, the distance must increase.Performance AssessmentStudents’ tables will vary. See expected outcomeon the Teacher Notes page for some examples ofpossible machines and their benefits.Analyze and Conclude1. Answers will vary. Sample: I would choosemy first-class lever made from a triangularblock and a rectangular block. It was simple tomake and had only two parts. It was the onlymachine I made that both multiplied the inputforce and changed the direction of the force.2. Answers will vary. Check students’ work.For an inclined plane, the ideal mechanicaladvantage is equal to the length divided by theheight. For a lever it is equal to the distance fromthe fulcrum to the input force divided by thedistance from the fulcrum to the output force.3. Answers will vary. Sample: I could combine the pulley and the wheels and axle. Insteadof pulling down on the pulley’s string to lift theweight, the string could be tied to the axle. Thenthe wheels could be turned to lift the weight. Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.

ANSWER KEYWork and MachinesJill did work.22. Jill performs 120 J of work. Eric performs 60J of work. Jill performs more work.23. Answers will vary. Sample: You wouldexert a force, but not do work when you hold aheavy bag of groceries. You would exert a forceand also do work when you lift that heavy bagof groceries out of a shopping cart.24. The six kinds of simple machines andexamples are: screw—jar lid; inclined plane—wheelchair ramp; pulley—flagpole; wedge—sharp knife; lever—baseball bat; wheel andaxle—bicycle25. A machine makes work easier by changingthe amount of force you exert, the distance overwhich you exert the force, or the direction inwhich you exert your force. A ramp lets youexert a smaller force over a larger distance. Thehigher gears on a bicycle let you apply a greaterforce over a shorter distance. A pulley lets youchange the direction over which you exert aforce.26. The ramp makes the work easier by multiplying the distance and reducing the requiredinput force.27. I.M.A. length of incline divided by heightof incline. 5 1.5 3.328. Because a machine makes work easier bychanging the direction or the amount of forceneeded29. The input and output forces are the same.Students’ examples may vary. Sample: a fixedpulley30. The more friction there is, the less efficienta machine is. You could make a machine moreefficient by reducing friction by lubricating themachine. Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.Work and MachinesChapter Test1. b2. a3. a4. d5. c6. d7. b8. a9. c10. b11. move some distance12. mechanical advantage13. axle14. tendons15. ideal mechanical advantage16. does not decrease17. screw18. true19. direction20. true21. Since the table and stool moved, Eric and

Work and Machines Work and Machines Chapter Project Worksheet 1 1. inclined plane, wedge, screw, lever, wheel and axle, pulley 2. pulley 3. lever 4. inclined plane 5. Answers will vary: top, side, or bottom 6. Answers will vary; only one of the six sim-ple machines must be mentioned. 7. Answers will vary; only one of the six sim-ple machines .