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P150_Exam3_F06

# P150_Exam3_F06 - Physics 151 December 4 2006 Exam#3 Name...

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Physics 151 Name______________________________ December 4, 2006 Exam #3 Lab Section Number________________ Instructions: There are 20 multiple choice questions (worth 2 points each), and 3 work problems (worth a total of 60 points). You must answer all questions to receive full credit. You must show all equations and substitutions made to obtain your answers for the work problems. Write the final answers to the problems with their respective units in the spaces provided. Part I (40) Part II (60) Total (100)

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Part I: Short Answers Multiple Choice: Please write in the letter of the item that best answers the question. 1.______ The total angular momentum of a system of particles is conserved if (A) the angular velocities of all particles in the system are constant. (B) the angular velocity of the center of mass of the system is a constant. (C) the rotational inertia of the system is a constant. (D) the net external torque is zero. (E) the net internal torque is zero. 2.______ A particle of mass m 1 is traveling with constant speed v clockwise around a circle of radius R 1 , in the xy plane and centered at the origin. A second particle, with mass m 2 , is traveling counterclockwise with the same speed around a concentric circle of radius R 2 . The total angular momentum along the z- axis about the origin of the two-particle system is (A) zero. (B) ( m 1 R 1 + m 2 R 2 )v. (C) ( m 1 R 1 - m 2 R 2 )v. (D) -( m 1 R 1 - m 2 R 2 )v. (E) (m 1 - m 2 )(R 1 + R 2 ) . 3.______ A child of mass m is running with constant speed v along a straight line that is tangent to the rim of a merry-go-round of radius R . The merry-go-round is turning about its center with constant angular velocity ω so that the point on the rim where the child will jump on is coming toward the child. The rotational inertia of the merry-go-round about its center is I . The total angular momentum of the system consisting of the child and the merry-go-round, about the center of the merry-go-round, is (A) I ω . (B) I ω + mv .
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