attenuation finding distace and amplitude

1. The problem statement, all variables and given/known data
problem 1
A 20 Hz seismic wave traveling at 3 km/s propagates for 2000 m from point X to point
Y through a medium with an attenuation rate of 0.5 dB/λ. What is the ratio between
the amplitude of the wave measured at X and the amplitude of the wave measured at Y (i.e., AX/AY)?

and
problem 2
A seismic wave travels from the source to two separate recording points in space following a single, straight ray path. The farhest recording point is located at 10km from the source and the signal is attenuated by 8dB between the two recording points. Assuming that all the attenuation is due to geometrical spreading, give the distance from the source to the nearest recoring point.

2. Relevant equations
LdB = 20log10(A1/A2), where LdB is a value of either attenuation or dynamic range that is given in decibels (dB).

3. The attempt at a solution
problem 1
i was thinking i somehow need to get rid of the λ behind 0,5dB.
λ=3000/20 = 150m and
2000/150 =13,33 λ from Ax to Ay….

problem 2
no idea.. tryed 8log = 20log10 (A0/A1)
(A1/A0)= 10^(8/20) = 2,512…..

i realy tryed to understand this for 3 days now and im going mad, if someone could show me how to solve this i will be verry grateful!

http://ift.tt/1evkELK

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