P.W.T. GUIDESHEET UNIT 2. - WORK SUBUNIT - WORK IN MECHANICAL SYSTEMS ACTIVITY LESSON DESCRIPTION SCORE/POINTS 1. NT NOTES: FILL IN GUIDE SHEET /10

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1 P.W.T. GUIDESHEET UNIT 2. - WORK PERIOD SUBUNIT - WORK IN MECHANICAL SYSTEMS ACTIVITY LESSON DESCRIPTION SCORE/POINTS 1. NT NOTES: FILL IN GUIDE SHEET /10 2. TX PP WORKSHEET /61 3. MS MATH PRACTICE /44 4.? s SECTION EXERCISES PP Do question 1,2, 4, 5,6,7,8 (2 pts each) /14 EXTRA CREDIT QUESTIONS 12, 14, 16 (4pts each show all work) /12 5. LB Rube Goldberg /66

2 MECHANICAL WORK NOTES Work = x Force is in or Distance is in or So Work is or Example 2A Given: a weight lifter raises a 200 lb barbell 5 ft. Find the work done: Example 2B Given: an electric truck uses 900 N. of force to move a cart 100 meters. Find the work done: Machines are rated by % Efficiency = = Work done by the machine. It s the final work being done or the reason you are using the machine. = Work you do to the machine. The work done on the machine to operate it. Example 2C Given: A block and tackle (pulley system) is used to lift an engine. The engine weighs 600 lbs and is raised 0.9 feet. The operator pulls with a force of 100 lbs over a distance of 6 ft. Find: input work, output work, and % efficiency Simple machines allow you to use less over a longer to accomplish a task.

3 The IMA (Ideal Mechanical Advantage) is a number that describes how much of an advantage (or how much less force you need to use) the simple machine will give if there is NO friction. For an inclined plane: Work Out = Force ( ) x Distance ( ) Work In = Force ( ) x Distance ( ) For a Lever: Work Out = Force ( ) Distance ( ) Work In = Force ( ) x Distance ( )

4 For a Pulley system: Work Out = Force( ) x Distance ( ) Work In = Force ( ) x Distance ( ) For the IMA, just count the Number of support strings.

5 WORKSHEET PP In mechanical systems, work is done when what? (1) 2. Write the equation for work and tell what each letter stands for (4) 3. In the English system, work is measured in (1) 4. In the SI system, work is measured in what 2 units?(2) 5. The distance and direction through which an object moves are also called its what? (1) 6. Explain the difference between positive work and negative work. (2) 7. Look at Example 2.1 then solve the following ( show: formula, work, answer, label= 4pts) Find the amount of work done by a weight lifter in lifting a 220 pound barbell a distance of 4 feet. 8. Why is no work done on the barbell while the weight lifter holds it in place above his head? (1) 9. What biological work is being done while holding a barbell? (1) 10. Look at example 2.2. Why is the answer negative? (1) 11. When you throw a ball the work done is force x distance. What distance do you use, the distance your arm went, or the distance the ball lands away from you? (1) 12. When the weight lifter does work on a barbell, the gravitational potential energy gained by the barbell equals what? (1) 13. When brakes slow down a cart, the cart loses kinetic energy. The amount of kinetic energy lost equals what? (1) 14. Machines are designed to do what? (2) 15. Output work is always than input work. (1) 16. Give an example of something that causes undesired but unavoidable losses of energy. (1) 17. Efficiency is a ratio of (1) 18. Output work is work done by what? (1) 19. Input work is work done on what? (1)

6 20. Write the formula to calculate percent efficiency (1) 21. Look at example 2.3 and then solve the following. Given: A block and tackle is used to lift and engine. The engine weighs 700 lbs and is moved 1.5 feet. The operator pulls with a force of 120 lbs over a distance of 10 feet. *1pt formula *1pt numbers in formula *1pt answer *1pt label Find Work Input. (4) Find Work Output (4) Find Efficiency in percent.(4) 22. To find work for a rotating object, instead of using force and distance you use what? (2) 23. The size of an angle can be shown in degrees, it can also be shown in (often abbreviated rad) (1) rev = degrees = rad (2) 25. The abbreviation for radian is. Since 3.14, 360 degrees = rad. (2) 26. A radian is not a "real" unit. A radian is the ratio of (1) 27. We drop the unit rad in a calculation unless the result is an quantity. (1) 28. What does the Greek letter "theta" look like? What does it stand for in the formula for work? (2) 29. Write the formula to find work in a rotational system. (1) 30. Look at example 2.4 and then solve the following: Given: A simple mechanical winch has a crank handle of 1 foot long. A force of 25 lbs is required to turn the crank. Find: How much work is done in the crank through 7 revolutions? Find Torque: (2) Find Total angle of revolutions in radians: (2) Find Work done: (4)

7 SECTION EXERCISES PP /14 1. (2 pts) 2. (2 pts) 4. (2 pts) 5. (2 pts) 6. (2 pts) 7. (2 pts) 8. (2 pts) EXTRA CREDIT QUESTIONS (4pts each show all work) /