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Ch6-HW4-solutions

# Ch6-HW4-solutions - louey(cal2859 Ch6-HW4 florin(56930 This...

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louey (cal2859) – Ch6-HW4 – florin – (56930) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points What is the condition necessary for an object to be in a bound state in terms of its kinetic energy K and its potential energy U , such as when a satellite orbits a planet or an electron orbits the nucleus of an atom? 1. K + U > 0 2. K U < 0 3. K + U + 0 4. K U > 0 5. K + U < 0 correct 6. K U = 0 Explanation: A system is in a bound state if the sum of its kinetic and potential energy is less than zero, i.e. K + U < 0, because the object does not have sufficient kinetic energy to escape the potential energy field. 002(part1of5)4.0points The figure below shows the path of a comet orbiting a star. A B C D E Rank-order the locations on the path in terms of the magnitude of the comet’s mo- mentum at each location, starting with the location at which the magnitude of the mo- mentum is the largest. 1. | vectorp E | > | vectorp D | > | vectorp C | > | vectorp B | > | vectorp A | correct 2. | vectorp D | > | vectorp E | > | vectorp C | > | vectorp B | > | vectorp A | 3. | vectorp A | > | vectorp B | > | vectorp C | > | vectorp D | > | vectorp E | 4. | vectorp E | = | vectorp D | > | vectorp C | > | vectorp B | = | vectorp A | 5. | vectorp A | = | vectorp B | = | vectorp C | = | vectorp D | = | vectorp E | Explanation: Momentum increases as the comet gets closer to the Sun; therefore | vectorp E | > | vectorp D | > | vectorp C | > | vectorp B | > | vectorp A | . 003(part2of5)4.0points Rank-order the locations on the path in terms of the comet’s kinetic energy at each location, starting with the location at which the kinetic energy is the largest. 1. K A >K B >K C >K D >K E 2. K E >K D >K C >K B >K A correct 3. K D >K E >K C >K B >K A 4. K E = K D >K C >K B = K A 5. K E = K D = K C = K B = K A Explanation: K increases as | vectorv | increases; therefore, K E >K D >K C >K B >K A . 004(part3of5)4.0points Consider the system of the comet plus the star. Which of the following statements are correct? List all that apply, separated by commas. If none apply, enter “none”. A. External work must be done on the sys- tem to speed up the comet. B. As the comet slows down, energy is lost from the system. C. As the comet’s kinetic energy increases, the gravitational potential energy of the system also increases.

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louey (cal2859) – Ch6-HW4 – florin – (56930) 2 D. As the comet slows down, the kinetic energy of the system decreases. E. As the kinetic energy of the system in- creases, the gravitational potential en- ergy of the system decreases. Correct answer: D, E. Explanation: The Sun can do work on the comet to in- crease its speed, so no external work is needed and statement A is false. And since the kinetic energy that is lost as the comet slows down simply becomes potential energy, statement B is false. Statement C is false because gravita- tional potential energy and kinetic energy are traded for each other—they can’t increase si- multaneously. The remaining statements are true.
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