A string of length 1.5 m with its two ends clamped is vibrating in fun...
Solution:
Given, length of the string, L = 1.5 m
Amplitude at the centre, A = 4 mm = 0.004 m
Amplitude at some point x from the centre, a = 2 mm = 0.002 m
We know that in a string vibrating in fundamental mode, the displacement y(x,t) can be given by the equation,
y(x,t) = A sin(kx) sin(ωt)
where, k = π/L and ω = πv/L
Here, v is the speed of the wave.
Let's find the value of v first.
We know that the wave speed, v = fλ
where, f is the frequency and λ is the wavelength.
In fundamental mode, the wavelength is twice the length of the string, i.e., λ = 2L.
Also, the frequency, f = v/λ = v/2L
Hence, ω = πv/L = 2πf
Now, let's find the value of k for the given string.
k = π/L = π/1.5 = 2.094 rad/m
Now, let's find the two points on the string where the amplitude is equal to 2 mm.
Let the distance of the first point from the centre be x1.
Then, a = A sin(kx1)
0.002 = 0.004 sin(2.094x1)
x1 = 0.2969 m
Similarly, let the distance of the second point from the centre be x2.
Then, a = A sin(kx2)
0.002 = 0.004 sin(2.094x2)
x2 = 1.2031 m
The minimum distance between the two points is given by,
d = x2 - x1
d = 1.2031 - 0.2969 = 0.9062 m
Therefore, the minimum distance between the two points having amplitude 2 mm is 0.9062 m, which is closest to option A (1 m).
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