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PHYSICS 6B
Ch.12 Worksheet Solutions
www.clas.ucsb.edu/staff/vince/
1)
Sound waves travel in air with a speed of 343 m/s. The lowest frequency
sound that the average person can hear is 20.0 Hz; the highest frequency is
20 kHz. Find the wavelengths corresponding to these frequencies.
We use the basic formula for waves:
With f=20Hz we get
λ
=17.2 m
With f=20kHz we get
λ
=17.2 mm
2)
A 12m rope is pulled tight with a tension of 92N. When one end of the
rope is given a “thunk” (disturbed from its equilibrium position) it takes
0.45s for the disturbance to propagate to the other end. What is the mass of
the rope?
We can use the formula for wave speed on a string:
Calculate speed=12m/0.45s=26.7 m/s, then plug in to find
m=1.5kg
3)
One of the harmonics on a string 1.3m long has a frequency of 15.6 Hz.
the next higher harmonic has
a frequency of 23.4 Hz. Find (a) the
fundamental frequency, and (b) the speed of the waves on this string.
Fundamental frequency is the difference between successive harmonics, so
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 Spring '11
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