The transverse displacement of a string (clamped at its both ends) is given by y(x,t)=0.6sin(2π3x)cos(120πt) where x and y are in m and t in s. The length of the string is 1.5m and its mass is 3.0×10−2kg.
Answer the following:
(a) Does the function represent a traveling wave or a stationary wave?
(b) Interpret the wave as a superposition of two waves traveling in opposite directions. What is the wavelength, frequency, and speed of each wave?
(c) Determine the tension in the string.
y (x, t) = 2asinkxcos ωt
This equation is similar to the equation:
y(x, t)=0.06 sin(2π3x)cos (120πt)
Hence, the given function represents a stationary wave.
A wave travelling along the positive x-direction is:
y1=a sin(ωt-kx)
The wave travelling along the negative x-direction is:
y2=a sin(ωt+kx)
The superposition of these two waves yields:
y=y1+y2=asin(ωt−kx)−asin(ωt+kx)=asin(ωt)cos(kx)−asin(kx)cos(ωt)−asin(wt)cos(kx)−asin(kx)cos(wt)=−2asin(kx)cos(ωt)=−2asin(2πλx)cos(2πνt) ...(i)
The transverse displacement of the string is:
y(x, t)=0.06sin(2π3x)cos(120 πt) ...(ii)
Comparing equations (i) and (ii),
Wavelength, λ=3 m
Frequency, ν=60 Hz
Wave speed, v=νλ=60×3=180 m/s
The velocity of a transverse wave travelling in a string:
v=√Tμ ...(i)
Velocity of the transverse wave, v = 180 m/s
Mass of the string, m = 3.0 × 102 kg
Length of the string, l = 1.5 m
Mass per unit length of the string, μ=ml=3.01.5×10-2=2×10-2 kg m-1
Tension in the the string,
T = v2μ
= (180)2 × 2 × 10-2
= 648 N
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