15.13 Given below are some functions of x and t to represent the displacement (transverse or longitudinal) of an elastic wave. State which of these represent (i) a travelling wave, (ii) a stationary wave or (iii) none at all:

(a) Y = 2 cos (3x) sin (10t)

(b) Y = 2

(c) Y = 3 sin (5x – 0.5t) + 4 cos (5x – 0.5t)

(d) Y = cos x sin t + cos 2x sin 2t

A set of 16 tuning forks are so arranged that each produce 4 beats with the previous one. If the frequency of last tuning fork is double that of first, the frequency of third tuning fork is

A pipe open at both ends produces a note of fundamental frequency V₁. When the pipe is kept with (1/3)^rd of its length in water, it produces a note of frequency V₂.The value of V₁/ V₂ is

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The value of restoring force constant is :-

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