su08Final

# su08Final - Physics 53 Summer 2008 Final Exam Solutions In...

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Physics 53 Summer 2008 1 Final Exam Solutions In questions or problems not requiring numerical answers, express the answers in terms of the symbols given, and standard constants such as g . If numbers are required, use g = 10 m/s 2 . Part A: Multiple choice questions. Check the best answer. Each question has a value of 4 points. 1. Which is a correct statement of a fundamental law of mechanics? If all the external forces on a system are conservative, total mechanical energy is conserved. If the total external force on a system is zero the total angular momentum about any point is conserved. If only conservative forces do work, the total linear momentum of the system is conserved. If any component of the total external force is zero, that component of the linear momentum is conserved. 2. In simple harmonic motion in one dimension: The acceleration and the displacement are always in opposite directions. The acceleration and the velocity are always in opposite directions. The velocity and the acceleration have their greatest magnitudes at the same time. None of the above is true. 3. A billiard ball (a solid sphere of radius R and mass m ) moves to the right across a rough table. It started without rotating, so it is still skidding, although eventually it will roll without slipping. Which of the following is NOT true? The torque about its CM is clockwise. Both its CM speed and its angular speed of rotation are decreasing. [Angular speed is increasing] It angular momentum about a point on the table is constant. Its total kinetic energy is decreasing.

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Physics 53 Summer 2008 2 4. Three objects (1,2,3) start from rest at the same time from the same height on an incline, and roll to the bottom without slipping. Their moments of inertia obey I 1 > I 2 > I 3 . The order of speeds with which they will reach the bottom is: 1,2,3 3,2,1 1,3,2 2,3,1 5. Shown is an auto with the normal forces on the front and rear wheels indicated. When the auto is at rest N 1 is somewhat larger than N 2 because the CM of the auto is closer to the front wheels. When the auto accelerates forward: Both normal forces remain the same. Both normal forces increase. N 1 increases while N 2 decreases. N 2 increases while N 1 decreases. [Consider torques about the CM.] 6. Concerning Kepler’s three laws, which of the following is NOT true? One law can be used to determine the mass of a planet if it has a moon. One law says that the quantity T 2 / a 3 ( T is the period, a the semi-major axis) is the same for the earth’s orbit around the sun and moon’s orbit around the earth. [Must orbit the same object] One law says the planetary orbits are ellipses with the sun at a focus. One law is equivalent to conservation of angular momentum of the orbit. 7. The change in internal energy of an ideal gas is given by ! U = nc V ! T : Only for processes at constant volume.
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## This note was uploaded on 10/19/2011 for the course PHYSICS 53L taught by Professor Mueller during the Spring '07 term at Duke.

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su08Final - Physics 53 Summer 2008 Final Exam Solutions In...

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