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Unformatted text preview: Alvarado, Patrick – Homework 7 – Due: Oct 26 2006, 10:00 am – Inst: Andrei Sirenko 1 This printout should have 18 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points Two objects, of masses 63 kg and 35 kg, are hung from the ends of a stick that is 70 cm long and has marks every 10 cm, as shown. 63 kg 35 kg A B C D E F G 10 20 30 40 50 60 If the mass of the stick is negligible, at which of the points indicated should a cord be attached if the stick is to remain horizontal when suspended from the cord? 1. C 2. A 3. F 4. E 5. G 6. B correct 7. D Explanation: Let : ‘ = 70 cm , m 1 = 63 kg , and m 2 = 35 kg . For static equilibrium, τ net = 0. Denote x the distance from the left end point of the stick to the point where the cord is attached. m 1 g x m 2 g [ ‘ x ] = τ = 0 ( m 1 m 2 ) x = m 2 ‘ x = m 2 ‘ m 1 m 2 = (35 kg)(70 cm) 63 kg 35 kg = 25 cm . Therefore the point should be point B . keywords: 002 (part 1 of 1) 10 points A wheel of radius R and negligible mass is mounted on a horizontal frictionless axle so that the wheel is in a vertical plane. Three small objects having masses m , M , and 2 M , respectively, are mounted on the rim of the wheel, as shown. 60 ◦ R M 2 M m If the system is in static equilibrium, what is the value of m in terms of M ? 1. m = 2 M 2. m = M 3. m = M 2 4. m = 5 M 2 5. m = 3 M 2 correct Explanation: Since the system is in static equilibrium, the net torque is zero: τ = mg R + M g R cos60 ◦ (2 M ) g R = mg R + 1 2 M g R 2 M g R Alvarado, Patrick – Homework 7 – Due: Oct 26 2006, 10:00 am – Inst: Andrei Sirenko 2 = mg R 3 2 M g R = 0 , so m = 3 M 2 . keywords: 003 (part 1 of 2) 10 points A student gets her car stuck in a snow drift. Not at a loss, having studied physics, she attaches one end of a rope to the vehicle and the other end to the trunk of a nearby tree, allowing for a small amount of slack. The student then exerts a force F on the center of the rope in the direction perpendicular to the cartree line as shown in the figure below. Assume equilibrium conditions and that the rope is inextensible. θ L d F How does the magnitude of the force ex erted by the rope on the car compare to that of the force exerted by the rope on the tree? 1. cannot be determined 2.  F t  =  F c  = T correct 3.  F t  = 2  F c  4.  F t  >  F c  5.  F t  <  F c  Explanation: Since the the student pulls on the center of the rope, we can readily see that angle between the rope and the car equals the angle between the rope and the tree. Hence  F t  =  F c  = T 004 (part 2 of 2) 10 points What is the magnitude of the force on the car?...
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This note was uploaded on 09/04/2008 for the course PHYS 106 taught by Professor Opyt during the Spring '08 term at NJIT.
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