An earthquake \"P\" wave passes across a boundary in rock where its velocity inc

Question

An earthquake "P" wave passes across a boundary in rock where its velocity increases from 6.0 km/s to 8.0 km/s. If it strikes this boundary at 30degree, what is the angle of refraction? 22 38 42 46 None of the Above During a lightning storm, the sound of thunder reaches your ear 11 seconds after you see the lightning. How far away is the lightning strike 3.0 km 3.8 km 5.1 km 31 km None of the Above At a busy street corner, the sound level is 130 dB. What is the intensity of sound in W/m^2? 1 times 10^1 1 times 10^0 1 times 10^minus1 1 times 10^minus2 None of the Above What is the new sound level when 10 students are talking given that each talks at the 100 dB level? 105 dB 110 dB 112 dB 115 dB 150 dB The sound level measured 20 in from a jet plane is 120 dB. What is the sound level at 300 m? (Ignore reflections from the ground.) 130 dB 120 dB 96 dB 70 dB 1 dB

Explanation / Answer

sintheta2/sintheta1 = v2/v1

theta2 = 41.8 degree =42 degree

part 2 )

d = v *t

v = 343 m/s * 11 = 3773 m = 3.773 km = 3.8 km

part 3 )

130 = 10log(I/Io)

Io =10^-12

13 = log (I/Io)

10^13 = I/Io

I= 10 W/m^2

part 4 )

I = 10I1

I = 10log(10I/Io)

I = 10log10 + 10log(I/Io)

I = 10 + 100 = 110 dB

part 5 )

120 = 10 log (I/Io)

I = 1 W/m^2

I is inversly proportional to r^2

I2/I1 = r1^2/r2^2

I2 = 4.44 x 10^-3

b = 10 log(4.44x 10^-3/10^-12)

b = 96.48 dB = 96 dB

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