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Homework Statement
A wave travels along a string in the positive x-direction at 30 m/s. The frequency of the wave is 50 Hz. At x = 0 and t = 0, the wave velocity is 2.5 m/s and the vertical displacement is y = 4 mm. Write the function y(x,t) for the wave.
Homework Equations
velocity = (wavelength)(frequency) = (angular velocity)/(wave number)
angular velocity = 2*pi*frequency
What the function should look like:
y(x,t) = Asin(kx - wt + θ)
A = amplitude
k = wave number
w = angular velocity
t = time (s)
θ = initial phase shift
The Attempt at a Solution
Figuring out the wave number (k) as well as the wavelength and angular velocity was the easy part:
w = 2*pi*(50 Hz) = 100*pi
wavelength = velocity/frequency = (30 m/s)/(50 Hz) = .6 m
wave number (k) = w/v = (100*pi)/(30 m/s) = 10.47 m^-1
So far the function looks like:
y(x,t) = Asin(10.47(x) - 314.16(t) + θ)
The only variables left to find are the amplitude (A) and initial phase shift (θ). I tried plugging in the initial conditions the problem gave me, but I end up with:
y(x,t) = Asin(θ) = .004
differentiating the function y(x,t) = Asin(10.47(x) - 314.16(t) + θ) with respect to time gives the velocity equation, which is:
v(x,t) = -A(314.16)cos(10.47(x) - 314.16(t) + θ)
and plugging in the initial conditions for velocity gives:
-A(314.16)cos(θ) = 2.5
I don't know where to go from here to find amplitude and the initial phase shift. I have tried setting the velocity equation equal to zero which would give me a critical point (amplitude), but that didn't help much. I've also tried using a substitution method between these two equations:
y(x,t) = Asin(θ) = .004
-A(314.16)cos(θ) = 2.5
but that didn't get me anywhere either. Any help would be greatly appreciated!