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Feb. 21 Mega Review Homework 1. Calculate the work done as a 100 N force pushes a crate 5 m along a floor. 2. Calculate the work done by a person who carries a 50 N box vertically 3m up a ladder. 3. What is the potential energy of the 50 N box when raised 3 m? 4. Calculate the power expended by the person who carries the 50 N box 3 m high in 3 s. 5. Calculate the kinetic energy of a 10 kg cart traveling at 4 m/s. 6. Calculate the change in KE when the speed of a 10 kg cart increases from 4 m/s to 10 m/s. 7. How much work is required to make the change in KE in the previous problem? HW Due #6-13 Ch 8 Guided Notes **Place both of these in In Box!** Tonight’s HW Read & Study p. 670-672. On p. 672, complete #1-7 ***WRITE the FULL Q&A. If you would rather print the questions, they are typed on my website – you may copy, paste, and print Ch 8 test on March 3 Do Now Take one Read the 1st column. Complete the 2nd Do Now Complete the 3rd column. You have all class to think about your response for the last column – that will be your exit for today (in addition to the back of this paper) Goals for Today 1. Concept Development– take a packet and complete. Check in at the stop signs. ***Not finished in class? Becomes HW!!! *** 2. Check your HW!!! – In groups, review the notes from last class that were also HW. Questions? Check with a teacher! – Check the book HW (#1-13, 21-23) with your groups. – Either today or next week, we will have time to clicker review all the HW as a class. Need help? ASK! 3. You will get back your Disney Quiz. You will have time to conference w/ teacher if you need help or clarification! 4. Finished? Complete the ***Boxed Questions on last class’ notes (all the questions before these were HW due today check in at STOP SIGNS!) ***These are NOT HW if not done in class we will finish these next week in class Take out your book HW • #1-4 • #5, 21-23 • #6-13 1. What do we call the quantity force times distance, and what quantity can it change? 1. 2. 3. 4. Work, energy Power, work Weight, energy Momentum, work 25% 1 25% 25% 2 3 25% 4 2. Work is required to lift a barbell. How many more times work is required to life the same barbell 3 times as high? 1. Half as much 2. Twice as much 3. Three times as much 4. Nine times as much 93% 0% 1 7% 2 0% 3 4 3. Which requires more work: lifting a 10 kg load a vertical distance of 2m, or lifting a 5kg load a vertical distance of 4m? A. lifting a 10 kg load a vertical distance of 2m B. lifting a 5kg load a vertical distance of 4m C. same work in both cases 56% 31% 13% A. B. C. 4. How much work is done on an object when a force of 10N pushes it a distance of 10m? A. B. C. D. 87% 1 Joule 1 Watt 100 Joules 100 Watts 13% 0% A. B. 0% C. D. 5a. How much power is required to do 100J of work on an object in 1 second? A. B. C. D. 56% 1 Joule 1 Watt 100 Joules 100 Watts 31% 6% A. 6% B. C. D. 5b. How much power is required to do 100J of work on an object in 0.5 second? 1. 2. 3. 4. 50 J 50 W 200 J 200 W 63% 26% 5% 1 5% 2 3 4 IMPORTANT! • SAME work… • HALF the time… • TWICE the power!!! Check Question!!! Work and Power are __proportional 1. Directly 2. Inversely 3. I have no idea 33% 1 33% 2 33% 3 Check Question!!! Time and Power are ___ proportional 1. Directly 2. Inversely 3. I have no idea 33% 1 33% 2 33% 3 POPCORN! 6. What are the 2 main forms of Mechanical Energy? (1 person will give one, and a 2nd person will give the other) 7a. If you do 100 J of work to elevate a bucket of water, what is its grav. PE relative to its starting point? 1. 2. 3. 4. More than 100 J Less than 100 J 100 J Zero 25% 1 25% 25% 2 3 25% 4 7b. If you lift it 2x as high, what’s its PE? 1. Less than 100 J 2. 100 J 3. More than 100 J, but less than 200 J 4. 200 J 5. More than 200 J 6. Zero 17% 1 17% 2 17% 17% 3 4 17% 5 17% 6 Check Question!!! Grav. PE and Height are ___ proportional 1. Directly 2. Inversely 3. I have no idea 33% 1 33% 2 33% 3 8. A boulder is raised above the ground so that its grav. PE is 200 J (relative to the ground). Then it’s dropped. What’s its KE the INSTANT just before hitting the ground? 25% 1. 2. 3. 4. 25% 25% 2 3 25% More than 200 J Less than 200 J 200 J Zero 1 4 9a. Suppose an automobile has 2000 J of kinetic energy. When it moves a twice the speed, what will be its kinetic energy? 25% 1. 2. 3. 4. 5. 6. The same (2000 J) 2x as much (4000 J) 3x as much (6000 J) 4 as much (8000 J) 6x as much (12,000 J) 9x as much (18,000 J) 1 25% 25% 2 3 25% 4 9b. Suppose an automobile has 2000 J of kinetic energy. What’s its kinetic energy at three times the speed? 25% 1. 2. 3. 4. 5. 6. The same (2000 J) 2x as much (4000 J) 3x as much (6000 J) 4 as much (8000 J) 6x as much (12,000 J) 9x as much (18,000 J) 1 25% 25% 2 3 25% 4 KE is directly proportional to the SQUARE of the velocity! 10. What will be the kinetic energy of an arrow having a potential energy of 50 J after it is shot from a bow? 25% 25% 25% 2 3 25% 1. The same (50 J) 2. More than 50 J 3. Less than 50 J 1 4 POPCORN 11. What does it mean to say that in any system the total energy score stays the same? POPCORN 11. What does it mean to say that in any system the total energy score stays the same? Energy is conserved. POPCORN 12. In what sense is energy from coal actually solar energy? POPCORN 12. In what sense is energy from coal actually solar energy? Coal is formed from organic material. Organic materials (plants, the animals that eat plants, and the animals that eat animals that eat plants) get their energy from the sun. POPCORN 13. How does the amount of work done on an automobile by its engine relate to the energy content of the gasoline? POPCORN 13. How does the amount of work done on an automobile by its engine relate to the energy content of the gasoline? It is less than the energy contained in the gasoline. An automobile engine is not 100% efficient. (Some of the gas energy powers the car…but some is transferred into heat, sound, etc… TOTAL ENERGY stays the same, but that sum is made of diff. types of energy!) CHECK QUESTIONS! Can energy ever be created? 100% 1. Yes 2. No 3. Sometimes 0% 1 0% 2 3 Can energy ever be destroyed? 89% 1. Yes 2. No 3. Sometimes 11% 0% 1 2 3 Does an object with momentum always have energy? 1. Yes 2. No 59% 41% 1 2 Does an object with energy always have momentum? 1. Yes 2. No 67% 33% 0% 1 2 3 If a mouse and an elephant both run with the same kinetic energy, can you say which is running faster? 60% 1. The mouse 2. the elephant 3. Not enough info to say 25% 15% 1 2 3 Using the diagram below… what happens to the skater’s KE as he goes DOWN the ramp? 1. Increases 2. Decreases 3. Stays the same 33% 1 33% 2 33% 3 Using the diagram below… what happens to the skater’s KE as he goes UP the ramp? 1. Increases 2. Decreases 3. Stays the same 33% 1 33% 2 33% 3 Using the diagram below… what happens to the skater’s PE as he goes DOWN the ramp? 1. Increases 2. Decreases 3. Stays the same 33% 1 33% 2 33% 3 Using the diagram below… what happens to the skater’s PE as he goes UP the ramp? 1. Increases 2. Decreases 3. Stays the same 33% 1 33% 2 33% 3 Using the diagram below… what happens to the skater’s TOTAL ENERGY as he goes UP the ramp? 1. Increases 2. Decreases 3. Stays the same 33% 1 33% 2 33% 3 Using the diagram below… what happens to the skater’s TOTAL ENERGY as he goes DOWN the ramp? 1. Increases 2. Decreases 3. Stays the same 33% 1 33% 2 33% 3