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Unformatted text preview: lew (dl9564) hk2 Opyrchal (41104) 1 This print-out should have 8 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A mass on a string is whirled in a vertical circle. What is the direction of the radial component of the acceleration vector at the instant shown in the diagram? v y x 1. None of these 2. + z 3. x correct 4. + y 5. + x 6. y 7. z Explanation: The radial acceleration is centripetal, i.e. in the x direction. 002 (part 2 of 2) 10.0 points What is the direction of the tangential compo- nent of the acceleration at the instant shown in the figure? 1. None of these 2. + z 3. y correct 4. z 5. + x 6. + y 7. x Explanation: The tangential acceleration is caused by the force of gravity, so it is in the y direction. 003 (part 1 of 2) 10.0 points Four particles with masses 8 kg, 2 kg, 8 kg, and 7 kg are connected by rigid rods of neg- ligible mass as shown. Assume the system rotates in the yz plane about the x axis with an angular speed of 5 rad / s. x y 5 rad / s O 5 rad / s 4m 4 m 8 kg 2 kg 8 kg 7 kg Find the rotational energy of the system about the x axis. Correct answer: 1250 J. Explanation: Let : m 1 = 8 kg , top left m 2 = 2 kg , bottom left m 3 = 8 kg , bottom right m 4 = 7 kg , top right s = 4 m , and = 5 rad / s . Each mass is a distance r = 2 m from the x-axis and summationdisplay m i = 8 kg+2 kg+8 kg+7 kg = 25 kg , so I x = summationdisplay m i r 2 i = r 2 summationdisplay m i = (2 m) 2 (25 kg) = 100 kg m 2 and the rotational energy of the system is...
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- Fall '08