NAME PERIOD P.O.T. GUIDESHEET UNIT 2. - WORK SUBUNIT - WORK IN MECHANICAL SYSTEMS ACTIVITY LESSON DESCRIPTION SCORE/POINTS 1. NT NOTES & STUDY QUESTIONS /20 2. WS PREVIOUS UNITS REVIEW /28 3. TX PP 84-89 READING GUIDE /40 4. MS PRACTICE MATH /48 5. LB A RUBE GOLDBERG MACHINE /66 Objectives: Explain work in mechanical systems Solve math problems using the formula Work = (Force)(Distance) W = FD Solve for Work In, Work Out, and % Efficiency for simple machines such as the Inclined Plane and various pulley systems Give the correct units for Work in both the English and SI systems Correctly interpret graphs and charts Correctly list the Independent, Dependent and Control Variables.
Name Period Score /20 5 points for notes filled in Work = MECHANICAL WORK NOTES Write at least 5 study questions From the notes (5 points) 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. 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.
5 points for notes filled in For an inclined plane: Work Out = Force Distance Write at least 5 study questions from the notes for this page (5 points) Work In = Force Distance For a Lever: Work Out = Force Distance Work In = Force Distance ( ) ( ) For a Pulley system: Work Out = Force Distance Work In = Force Distance For the IMA, (ideal mechanical advantage) just count the number of support strings.
PREVIOUS UNITS REVIEW 28 points 1. There is a force of 24 N between 2 masses. If the distance between the mass is doubled, (so 2 times farther apart) what is the new force between them? (2pts) 2. There is a force of 24 N between 2 masses. If the amount of one mass is doubled, what is the new force between them? (2pts) 3. There is a force of 24 N between 2 masses. If the distance between the mass is cut in half, (so 2 times closer together) what is the new force between them? (2pts) USE THE FOLLOWING PICTURE FOR THE NEXT 4 QUESTIONS Two electrical charges are shown in the diagram. 4. How would the strength of the electrostatic force (electrical force) change if Q1 were doubled? (1pt) 5. How would the strength of the electrostatic force change if d were doubled? (1pt) 6. How would the strength of the electrostatic force change if Q1 were half as much?(1pt) 7. How would the strength of the electrostatic force change if d were cut in half? (1pt) 8. Write which type of heat transfer is mostly responsible for each of the following: Choose from: Conduction, Convection, and Radiation (10 pts total = 1 pt each) A. The air near the ceiling is normally warmer than air near the floor. B. You feel the heat from a bonfire even though you are several meters away from it. C. You can boil water in a microwave oven. D. Smoke rises up a chimney. E. The handle of a metal spoon becomes hot when you use it to stir hot soup. F. The air above a campfire is hot. G. You touch a hot stove and get burned.
H. Heat lamps over the Pizza s keep them warm. I. Earth s crustal plate movement because of currents in the liquid mantle J. Energy from the sun is able to travel through space to the 9. Two people are pushing on an object in the same direction. One person applies a force of 500 Newton s to the object while the other applies a force of 700 Newton s. A third force (which is friction) of 400 Newton s acts on the car but in the direction opposite to that of in which the people or pushing. a. Draw a vector diagram (a picture with vector arrows) showing the 3 forces. (1pt) (in the space on the right) b. What is the net force on the object? (1pt) 10. A light that weighs 50 Newton s hangs from the ceiling on a chain. a. In the space to the right, draw a vector diagram of the forces acting on the light. (1pt) b. How much force does the chain exert on the light? (1pt) c. What is the net force acting on the light? (1pt) 11. Two forces act on an object with forces of 20 N and 15 N. These forces are applied at different directions to the object as described below. Solve for the total force acting on the object for each situation. a. The 2 forces act exactly opposite directions (1pt) b. The 2 forces act in the exact same direction (1pt) c. The 2 forces act at right angles. (you could draw and measure or use a 2 + b 2 = c 2 ) (1pt)
WORKSHEET PP. 84-93 1. 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 hold 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) 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)
FORCE WORK Distance % Efficiency = Work Out x 100 Work In PRACTICE MATH WORKSHEET 1. A horizontal force of 50 Newtons is applied to push a desk 25 meters across a warehouse floor. FIND THE WORK DONE 2. A test shows that 200 ftlb of work is required to lift an object a distance of 5 feet. FIND THE WEIGHT (FORCE) OF THE OBJECT a. Write the formula to find force (weight)(1pt) 3. A pulley system lifts a 400 lb weight a distance of 2 feet. The operator pulls the rope with a force of 80 lbs. a distance of 12 feet. Solve for the following: WORK OUT WHAT THE PULLEY DOES WORK IN WHAT THE OPERATOR DOES % EFFICIENCY a. Write the formula to find efficiency (1pt) 4. If you find that you have 850 Nm of output work and 900 Nm of input work, calculate the percent efficiency. a. Write the formula to find efficiency (1pt)
5. A person uses an inclined plane to move a box 3 feet up off the ground into the back of a pickup truck. The box weighs 220 pounds. The inclined plane is 9 feet long and the person pushes the box up that inclined plane with a force of 100 pounds. Solve the following: WORK OUT THE BOX FROM THE GROUND TO THE TRUCK. WORK IN WHAT THE PERSON DOES % EFFICIENCY a. Write the formula to find efficiency (1pt) 6. A person uses a lever to raise a 400 Newton box up a distance of 0.5 meters. The person has to push down on the lever with a force of 200 Newtons a distance of 1.5 meters. Solve the following. WORK OUT WHAT HAPPENS TO THE BOX WORK IN WHAT THE PERSON DOES % EFFICIENCY a. Write the formula to find efficiency (1pt)