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su10FinalS

# su10FinalS - Physics 53 Summer 2010 Final Exam Solutions...

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Final Exam Solutions Part A. Multiple choice questions. Check the best answer. Each question carries a value of 4 points. 1. A particle moves subject to a constant acceleration a . Its trajectory must be a straight line along the line of a . It will not move exactly in a circle. [Its direction must change.] If it starts from rest, the distance it moves in the first second is half the distance it moves in the second one. [One third.] Its speed must increase linearly with time. [Depends on direction of v .] 2. A system is subject to zero net external force. Its total momentum and angular momentum are certainly conserved, but its total mechanical energy might not be. Its total momentum, angular momentum and mechanical energy are all certainly conserved. Its total momentum is certainly conserved, but its total angular momentum and mechanical energy might not be. None of the three quantities is certainly conserved. Physics 53 Summer 2010 1

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3. Concerning a rigid body rolling without slipping on a surface, which of the following is wrong? If the CM speed is not equal to the angular speed times the radius of the body, it will slip. If the total external force on the body is zero, the total external torque about the CM must be zero in order for it to continue to roll. The ratio of kinetic energy of rotation to that of translation varies with the speed. It cannot roll freely without slipping down a frictionless incline. 4. A figure skater starts a slow spin standing on the tip of one skate with the other leg and both arms extended. As she pulls the leg and arms close to her body she spins faster because: Energy is conserved while the moment of inertia about the rotation axis decreases. External torques exerted by the ice cause an angular acceleration. Angular momentum about the rotation axis is conserved while the moment of inertia about that axis decreases. None of the above is the reason. 5. Concerning tidal forces acting on the earth, which of the following is wrong? The effect of the moon is stronger than that of the sun despite the fact that the sun is much more massive. The moon’s tidal effect on the side of the earth opposite the moon is approximately equal to its effect on the side nearest the moon. The tidal effect arises because the gravitational fields of the moon and sun are stronger on one side of the earth than on the other. Large “spring” tides occur only at full moon. [Also new moon.] Physics 53 Summer 2010 2
6. A violin string is played simultaneously with a tuning fork of frequency 440 Hz, producing 4 beats per second. If the tension in the string is increased, the beats disappear. The initial frequency of the violin string was: 444 Hz 442 Hz 438 Hz 436 Hz [Increasing tension increases frequency.] 7. Containers A, B, and C have identical amounts of an ideal gas at pressure P and volume V. In all three the pressure is raised to 2P. In A it is done at constant volume, in B adiabatically, and in C isothermally. The entropy changes in the three cases rank, from lowest to highest, as follows: [Consider dQ. ]

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su10FinalS - Physics 53 Summer 2010 Final Exam Solutions...

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