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Unformatted text preview: pokharel (pp7242) – Waves and Sound – walther – (16180) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. First Assignment 001 10.0 points Sound in air can best be described as which of the following type of wave? 1. Electromagnetic 2. Torsional 3. Polarized 4. Longitudinal correct 5. Transverse Explanation: A sound wave in the air is propagated by the oscillation of air molecules. It is best described as longitudinal wave. 002 (part 1 of 2) 10.0 points A standing wave of frequency 5 hertz is set up on a string 2 meters long with nodes at both ends and in the center, as shown. 2 meters Find the speed at which waves propagate on the string. 1. 5 m / s 2. 20 m / s 3. 10 m / s correct 4. 2 . 5 m / s 5. . 4 m / s Explanation: Let : f = 5 Hz and λ = 2 m . The wavelength is λ = 2 m, so the wave speed is | vectorv | = f λ = (5 Hz)(2 m) = 10 m/s . 003 (part 2 of 2) 10.0 points Find the fundamental frequency of vibration of the string. 1. 2 . 5 Hz correct 2. 5 Hz 3. 1 Hz 4. 7 . 5 Hz 5. 10 Hz Explanation: 2 meters The fundamental wave has only two nodes at the ends, so its wavelength is λ = 4 m and the fundamental frequency is f = v λ = 10 m / s 4 m = 2.5 Hz . 004 10.0 points The graph below represents the potential en- ergy U as a function of displacement x for an object on the end of a spring ( F =- k x ) oscillating in simple harmonic motion with amplitude x max . pokharel (pp7242) – Waves and Sound – walther – (16180) 2 + x max- x max x U U max Which graph represents the kinetic energy K of the object as a function of displacement x ? 1. + x max- x max x K K max 2. + x max- x max x K K max 3. + x max- x max x K K max 4. + x max- x max x K K max correct 5. + x max- x max x K K max 6. + x max- x max x K K max 7. + x max- x max x K K max Explanation: At the equilibrium point ( x = 0), the veloc- ity is maximum and the kinetic energy is U max due to conservation of energy. At the max- imum displacement points + x max and- x max the velocity is zero and the kinetic energy is zero. From a different perspective, in simple har- monic motion of an object on the end of a spring, the total energy is conserved. At the maximum displacement x max , the kinetic en- ergy is 0, so E = U ( x max ) = U max . U + K = E = U max K ( x ) = U max- U ( x ) . Thus, K ( x ) looks like an upsidedown U ( x ). 005 10.0 points An ideal massless spring is fixed to the wall at one end, as shown below. A block of mass M attached to the other end of the spring oscillates with amplitude A on a frictionless, horizontal surface. The maximum speed of the block is v m ....
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This note was uploaded on 06/07/2010 for the course PHYSICS 58930 taught by Professor Kleinman during the Fall '09 term at University of Texas.
- Fall '09