1 NAME PERIOD PHYSICS GUIDESHEET UNIT 5. - ENERGY SUBUNIT - ENERGY CONVERSIONS POTENTIAL AND KINETIC ENERGY ACTIVITY LESSON DESCRIPTION SCORE/POINTS 1. NT CLASS OVERHEAD NOTES (5 pts/page) /20 (Plus 5 pts/page for sample questions) /20 2 foldables 10 pts each /20 2. TX PP 230 239 READING GUIDE /31 3. TX PP 243-253 READING GUIDE /39 4. WS REVIEW QUESTIONS/MATH WS /75 5. WS REVIEW WORKSHEET /57
2 GRAVITATIONAL POTENTIAL ENERGY NOTES Energy that is stored by lifting it to a higher position. The formula to find GPE is Write a sample test questions next to your notes on this side You lift a 50 pound box to a shelf that is 5 feet high. How much work did you do to lift it? How much potential energy is stored in the box? **This shows that the work done to lift the box is stored in the box as potential energy. A 2 kg box is on a shelf 3 meters high. How much potential energy does it have? (gravity = 9.8 m/sec) A 8 kg rock balances on a ledge 50 meters high. Find the gravitational potential energy. (gravity = 9.8 m/sec) LINEAR KINETIC ENERGY NOTES The formula to find kinetic energy is: A hammer with a mass of 2 kg is moving 4 meters/sec. How much kinetic energy does it have?
If you double the mass to 4 kg, and it still moves 4 m/s, How much kinetic energy? 3 Write a sample test questions next to your notes on this side What if you double the speed from 4 meters/sec to 8 meters/sec. The mass is still 2 kg. What is the kinetic energy? A person and bicycle together have a mass of 600 kg. If they are traveling at 8 meters/sec, how much kinetic energy do they have? ELASTIC POTENTIAL ENERGY NOTES When you stretch an elastic or a spring, it wants to return to its unstretched or equilibrium position. The force needed to stretch the spring or elastic depends on: This is called the. The letter stands for the spring constant. The formula to find k is: The potential energy stored in a spring or elastic depends on: So the formula to find PE elastic is: When a force of 30 Newtons is applied to a spring, it moves a distance of 0.5 meters. What is the spring constant?
How much potential energy is there in a spring that is stretched 0.5 meters, if the spring constant is 60 N/m? 4 Write a sample test questions next to your notes on this side How much potential energy is there if you stretch the spring 2 times as far? (1.0 meters) How much potential energy is there if you stretch the spring 3 times as far? (1.5 meters) ENERGY IN ROTATIONAL SYSTEMS ROTATIONAL INERTIA The resistance of an object to changes in its Also called the Depends on the distribution of mass. EXAMPLES: 1. Baseball bat - longer bat harder to get moving than short. 2. Tight rope walker - long poll increases inertia and lets him balance easier. 3. Bending legs when running. - easier to swing back and forth.
5 Different shapes have different moments of inertia, so different formulas to calculate. Write a sample test questions next to your notes on this side To find rotational kinetic energy you use this formula: A bowling ball with a mass of 7 kg and a radius of.125 meters is turning 30 rad/sec. Find the rotational kinetic energy. ANGULAR MOMENTUM = ROTATIONAL INERTIA X VELOCITY It must be conserved. If rotational inertia decreases (smaller diameter) then velocity increases. Examples
6 SECTON 5.1 Reading Guide 230 239 1. What is kinetic energy? (1) 2. Write the formula for kinetic energy and tell what each letter means. (4) 3. The unit for kinetic energy is the same as the unit for what? (1) 4. In SI, kinetic energy is measured in what? (1) 5. What are the English units for energy? (1) 6. Kinetic energy increases with the mass. Give an example. (2) 7. Kinetic energy increases with the of the speed. Give an example (2) 8. Look at Example 5.1 then solve the following: After a serve, a 0.27 kg volley ball is moving 20 m/s. What is the kinetic energy of the ball? (4) 9. Write the formula to find the kinetic energy of a body in rotation and tell what each letter means. (4) 10. The moment of inertia of a body in rotational motion is usually what? (1) 11. Write the formula to find the moment of Inertia for a: particle in circular orbit, a solid sphere, and a hollow sphere. (3) 12. Moment of Inertia is a property that describes what? (1) 13. Write the formula to find work using kinetic energy. (1) 14. What is the work-energy theorem? (1)
7 SUMMARY (read summary p. 239 and fill in answers below) 15. Energy is a property that what? (1) 16. Kinetic energy is what? (1) 17. The moment of Inertia is a property that describes what? (1) 18. When work is done on an object, its kinetic energy changes by what? (1) SECTION 5.2 Reading guide pp. 243 253 1. When you toss a ball in the air, you give it energy. (1) 2. At the highest point it stops move upwards. Its kinetic energy is what? (1) 3. What force causes the ball to stop and then come back down? (1) 4. As the ball rises, it gains the to do work. (1) 5. The amount of work the ball can do because of its height above your hand is called what? (1) 6. Write the formula to find gravitational potential energy and tell what the letters mean. (4) 7. What are the units for potential energy in SI and English? (2) 8. In calculation of gravitational potential energy, the height h is measured from what? (1) 9. When you specify a reference level, you are defining the potential energy to be what? (1) 10. An object or fluid has potential energy because of its position in the Earth s what? (1) 11. It is more accurate to say the has potential energy. (1)
8 12. Explain how the forces of the Earth and an object interact. (2) 13. What is restoring force? (1) 14. What is elasticity? (1) 15. The elasticity of a spring is due to what? (1) 16. What is the equilibrium position? (1) 17. What happens when you push or pull a spring from the equilibrium position? (1) 18. Most springs exert restoring forces that are what? (1) 19. What happens if you compress or extend a spring past the elastic limit? (1) 20. What does the spring constant tell you? (1) 21. Work is stored in a spring as what? (1) 22. Write the formula to find Elastic Potential Energy and tell what the letters mean. (4) 23. Give 4 examples of uses for elastic potential energy. (4) 24. Total energy is not lost, it is what? (1) 25. Write the law of conservation of energy. (1) 26. Explain how conservation of energy applies when you toss a ball straight up in the air. (3)
9 REVIEW QUESTIONS / 75 POINTS 1. A pile driver hammer stores 100 ft lb of potential energy when the hammer is raised 0.25 ft. How much does the hammer weigh? (show work - 4pts) 2. A block with a mass of 10 kilograms is located 30 meters above a road. If the block fell, what would be its kinetic energy at the moment it struck the ground? Gravity = 9.8 m/sec 2 (assume no losses from air friction) (show work - 4pts) (solve for potential energy which converts to kinetic) 3. A system has a total energy of 600 ftlb. If there are no losses of heat, and 250 ftlb is potential energy, describe the amount and type of energy remaining in the system. (2pts) 4. A motorcycle front wheel spring shock has a spring constant of k = 300 pound/inch. The spring is compressed 2 inches beyond its normal resting position while going over a large rock. How much potential energy is stored in the spring? (show work 4pts) ** get answer units of inch pound, then divide that answer by 12 to get ft lb** 5. A construction elevator raises a 300 pound load of bricks from the ground to the third floor of the building, 24 feet above the ground. Find the potential energy of the load of bricks when it reaches the third floor. (show work 4pts) 6. A newspaper printing machine uses a set of rollers to feed paper through the machine. The rollers are held firmly against the paper by a spring. The spring exerts a force of 100 pounds when it is compressed 4 inches beyond its unstretched length. a. Find the spring constant (k) that the maintenance technician should specify when ordering a spare replacement. (show work 4pts) b. Find the amount of potential energy stored in the spring when it is compressed the spring 4 inches. (show work 4pts)
10 7. Data showing typical ball speeds for different sports: Fill in the kinetic energies of each ball just after it is struck. (12pts) KE = ½ mv 2 Ball Ball mass Ball velocity KE (kg) (m/s) before (m/s) after After ball is struck Tennis ball 0.058 0 51 Squash ball 0.032 0 49 Hand ball 0.061 0 23 Golf ball 0.046 0 69 Football kick 0.42 0 28 Cricket ball 0.16 0 39 (Data taken from : Physics, R. Hutchins, University of BATH, Thomas Nelson & Sons Ltd., 1992) 8. Knowing that the potential energy at the top of the tall platform is 50 J, what is the potential energy at the other positions (A-F) shown on the stair steps and the incline? (Each step is the same height) (10 points) Label on the chart for each step. Assuming there are no losses of energy due to friction, what is the Kinetic Energy at Positions A? C? E? F?
9. A cart is loaded with a brick and pulled at constant speed along an inclined plane to the height of a seat-top. If the mass of the loaded cart is 3.0 kg and the height of the seat top is 0.46 meters, then what is the potential energy of the loaded cart at the height of the seat-top? (4points) 11 10. If a force of 15.0 N is used to drag the loaded cart (from previous question) along the incline for a distance of 0.90 meters, then how much work is done on the loaded cart? (4 points) (Note that the work done to lift the loaded cart up the inclined plane at constant speed is equal to the potential energy change of the cart.) 11. Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s. (4points) 12. If the roller coaster car in the above problem were moving with twice the speed, then what would be its new kinetic energy? (4points)
12 13. Classify each of the following according to the type of energy. Write the letter of the correct response to the left of the number. (1 pt. each 11 total) 1. Water in a reservoir behind a dam. A. Gravitational Potential 2. Hydrogen found within the sun. 3. Batteries for a CD player. B. Elastic Potential C. Chemical Potential 4. Rock on a cliff. D. Electrostatic Potential 5. A stretched scale spring. 6. A flywheel that is spinning. E. Nuclear Potential F. Kinetic Energy 7. A bungee cord, when the jumper is at the lowest position, and the cord is stretched 8. A pendulum at the bottom of its swing. 9. When positive and negative charges are separated from one another in a capacitor. 10. A skier sliding down a hill. 11. Rubbing a balloon through your hair, then holding it a few centimeters to the side of your hair.
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16 ENERGY FORMULAS Gravitational Potential Energy Weight Height GPE = w h GPE = m g h Mass Weight Gravity 9.8 m/sec2 Weight = m g Work Force Distance Work = F x D Elastic Potential Energy ½ spring constant 1/2 k distance 2 d 2 PE elastic = ½ k d 2 Linear Kinetic Energy ½ mass velocity 2 KE = ½ m v 2 k spring constant Force k = f d d distance Rotational Kinetic Energy ½ moment of inertia KE = ½ I ω 2 angular velocity squared (rad/sec)2