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Unformatted text preview: Exam Phys 2C Name__Mechanical waves_________________________________ MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) Which of the following is a WRONG statement? A) When you play a guitar and clamp a string with your finger, you produce a note with a different frequency, because you change the wave speed. B) Light waves propagate faster than sound waves. Therefore, if a sound wave and a light wave have the same frequency, the sound wave has a smaller wavelength. C) Waves on the surface of water are neither purely longitudinal nor purely transverse. D) Two small- amplitude harmonic waves propagating on the same string should have the same wave speed. 2) Which of the following is a WRONG statement A) If a spherical wave propages in a medium without losing its total power, its intensity varies as an inverse square of the distance from the wave source. B) Two waves along the x- axis producing disturbances y(x, t) = 3 · sin(2x- 3t) and y(x, t) = 8 · sin(4x- 6t) have different wave speeds. (Here x is the position, t is the time, and all coefficients are in SI units.) C) If the amplitude of a wave on a given string is reduced to a half, while the frequency and the tension force remain unchanged, the power of the wave is reduced to a quarter. D) When you tune a guitar, you change the tension of the strings, thus varying the speed of transverse waves on them. 3) Which of the following is a WRONG statement? A) A smaller wave number corresponds to a greater distance between adjacent wave crests. B) The equation y(x, t) = A · exp[- (x- bt) 2 ] corresponds to a bell- shaped pulse running in the positive x direction with a wave speed b. C) For waves with a given wave speed, higher frequency corresponds to lower wave number. D) The wave speed of a pulse can be measured as the distance traveled by the crest of the pulse divided by the time its takes to travel this distance. E) In a longitudinal wave the speed of the wave and the speed of motion of material particles are different entities. 4) A simple harmonic wave with a frequency of 230 Hz and amplitude of 1 mm is propagating along a string in the negative x- direction at a speed of 45 cm/s. What is the wave number in m- 1 ? A) 1400 B) 2200 C) 5500 D) 1200 E) 3200 5) A string, 80 cm long and having a mass of 61 g, is attached to a 660- Hz vibrator at one end. The other end of the string is fixed and the string is kept under tension. The vibrator produces a transverse wave in the string, whose amplitude is 5.0 mm, and that propagates with a velocity of 32 m/s. The energy of the wave is absorbed at the fixed end. In this situation, the tension in the string, in SI units, is closest to: A) 87 B) 78 C) 75 D) 81 E) 84 A-1 6) The equation y ( x,t ) = 0.02 sin(6 x + 144 t ), where all quantities are in SI units, represents a traveling wave on a string having: A) wavelength = 38 B) the maximal velocity of motion of a segment of the string = 2.88 C) frequency...
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This note was uploaded on 12/13/2011 for the course PHYS 2C PHYS 2C taught by Professor Groisman during the Spring '11 term at UCSD.
- Spring '11