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Question
A string 1 m long is fixed at one end. The other end is moved up and down with a frequency of 20 Hz. Due to this, a stationary wave with four complete loops gets produced on the string. Find the speed of the progressive wave which produces the stationary wave.
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Solution
L = 1 m, n = 20 Hz
Since an antinode is formed at the free end.
Thus, with four and a half loops of the string,
L = `λ/4 + 2λ = 9/4λ`
∴ λ = `(4"L")/9 = 4/9 xx 1 = 4/9`m
∴ v = nλ
= `20 xx 4/9`
= 8.88 m/s
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