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Unformatted text preview: madrid (tmm2353) HW 7-4 Antoniewicz (56445) 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 3) 10.0 points A spring with stiffness 880 N / m and relaxed length 1 . 1 m stands vertically on a table. You hold a block of mass 2 kg, barely touching the top of the spring. Suppose you let the mass down onto the spring a certain distance very slowly and ob- serve that the mass is not moving (not oscil- lating) at this point. How much did the spring compress? Use g = 9 . 8 m / s 2 . Correct answer: 0 . 0222727 m. Explanation: Suppose x eq is the amount by which the spring is compressed. Since the mass is not moving (i.e. the mass is in equilibrium)at the final position, the net force on the mass is zero at this point. Therefore, k x eq = M g, which can be rearranged to, x eq = M g k = (2 kg)(9 . 8 m / s 2 ) 880 N / m = . 0222727 m . 002 (part 2 of 3) 10.0 points How much work did you do on the spring-mass system in the process? Correct answer:- . 218273 J. Explanation: The total initial energy is, E i = K + U gravity + U spring = 0 + Mgx eq + 0 = M 2 g 2 k . Similarly, the total final energy is, E f = 1 2 kx 2 eq = 1 2 M 2 g 2 k . Note that the zero for the gravitational po- tential energy is set at the final position of the mass....
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- Fall '08