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Sample Solutions
Physics I Honors

Wilson & Buffa:  College Physics

Set 6

Chapter 13, Exercises: pg 444-445 #79, 80
79

(a) 8.49 m/sec
(b) 0.424n hz [where n is a whole number]

To solve this problem we will use the formula vw = SQRT [ Tension / (mass/length) ].

The linear mass density, or mass per unit length (mass/length), of the tubing is given as 0.125 kg/m.  The tension in the tubing is given as 9 newtons, 9 N.

vw = SQRT [ 9 / (0.125) ] = SQRT (72) = 8.49 m/sec

To determine the natural frequencies of the tubing, we must first determine its fundamental frequency. All natual resonance frequencies will be multiples of this value.

The fundamental frequency will have one loop in its waveform.  That loop equals 1/2 the fundamental wavelength.  If the tubing is 10 meters long, then 1/2 l = 10  ® l = 20 meters.

Using vw = fl ® f =8.49 / 20 = 0.424 hz

80 10 hz, 20 hz, 30 hz, 40 hz

To solve this problem we will use the formula vw = SQRT [ Tension / (mass/length) ].

The linear mass density, or mass per unit length (mass/length), of the string is given as 2.5 x 10-2 kg/m.  The tension in the string is given as 40 newtons, 40 N.

vw = SQRT [ 40 / (0.025) ] = SQRT (1600) = 40.0 m/sec

To determine the natural frequencies of the string, we must first determine its fundamental frequency. All natural resonance frequencies will be multiples of this value.

The fundamental frequency will have one loop in its waveform.  That loop equals 1/2 the fundamental wavelength.  If the string is 2.0 meters long, then 1/2 l = 2.® l = 4.0 meters.

Using vw = fl ® f = 40.0 / 4.0  = 10.0 hz

NOTE Additional problems using the formula vw = SQRT [ Tension / (mass/length) ] can be found on the extra practice worksheet.