4) Two identical sinusoidal waves travel in the same direction at the same speed with an amplitude A. The phase difference between the two waves is o is increased with respect to the amplitude of the individual waves, A, by: 69.8. The amplitude of the resultant wave, Aresultant (a) 18% (b) 64% (c) 82% (d) 164% 5) Two identical sinusoidal waves with frequency of 20 Hz travel in the same direction at the same spee The two waves originate from the same point but with a time difference At. The amplitude of th AV3. The minimum possible time difference between the starting moments resultant wave is Ares the two waves is, At =: (a) 1/120 sec (b) 0.477 sec (c) 1/80 sec (d)0.716 sec

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9. A plane seismic wave, travelling vertically downwards in a rock of density 2200 kg m-3 with seismic velocity 2000 m s-1, is incident on the horizontal top surface of a rock layer of density 2400 kg m-3 and seismic velocity 3300 m s-1. (a) What are the amplitude ratios of the transmitted and reflected waves? (b) What fraction of the energy of the incident wave is transmitted into the lower medium?

A wave is described by the equation: with t in seconds and x in metres. (i) € (iv) y(x, t) = 0.6 sin[(2t - 6x) + +핑 Find the frequency, wavelength and wave number of this wave [Hint: write (2t-6x) as -(6x-2t) and then use trigonometric identities to interpret what y(x,t) = Asin[-(kx-ot)] represents graphically compared to y(x,t) = Asin(kx-cot). What is the propagation velocity/wave speed of this wave? What is the displacement and velocity of a particle at x = 0,3 m at t = 2 s? Based on your answer in (c) above, is the particle at x = 0,3 m moving away or towards the equilibrium at t = 2 s? Explain.