(a) Show that for a wave on a string, the kinetic energy per unit length of string is where is the mass per unit length of string is

(b) Calculate for a sinusoidal wave given by Eq. (15.7).

(c) There is also elastic potential energy in the string, associated with the work required to deform and stretch the string. Consider a short segment of string at position x that has un-stretched length as in Fig. 15.13. Ignoring the (small) curvature of the segment, its slope is Assume that the displacement of the string from equilibrium is small, so that has a magnitude much less than unity. Show that the stretched length of the segment is approximately

Figure 15.13:

(d) The potential energy stored in the segment equals the work done by the string tension F(which acts along the string) to stretch the segment from its un-stretched length Dx to the length calculated in part (c). Calculate this work and show that the potential energy per unit length of string is

(e) Calculate u_p(x, t) for a sinusoidal wave given by Eq. (15.7).

(f) Show that u_k(x, t), = u_p (x, t), for all x and t.

(g) Show y(x, t), u_k(x, t), and u_p (x, t) as functions of x for in one graph with all three functions on the same axes. Explain why u_k and u_p are maximum where y is zero, and vice versa.

(h) Show that the instantaneous power in the wave, given by Eq. (15.22), is equal to the total energy per unit length multiplied by the wave speed v. Explain why this result is reasonable.

Transcribed Image Text:

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