Задача 40588.

The flat sound wave whose equation in SI units is given by: y (x, t) = 2,5 * 10 ^ -6 * cos10 ^ 3 Pi (t- (x / 330)) is distributed in the air density is 0.0012 g / cm ^ 3. Determine the energy beig wave for one minute through the area 12 cm ^ 2, perpendicular to the wave propagation. In solving the problem, note that the mean square of the sine of the period is 0.5.

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