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**Q.**An ultrasound shock wave is incident on a kidney stone which is immersed in urine. Using the data below, calculate the critical angle at the urine-kidney stone interface, and thus

__estimate the energy that will be delivered to the spherical stone__. Assume intensity is uniform across the stone.

[tex]\rho_{urine} = 1000kg/m^{3},

c_{urine} = 1000m/s,

\rho_{stone} = 2000kg/m^{3},

c_{stone} = 4000m/s[/tex]

Diameter of kidney stone [tex]d = 10mm[/tex]

RMS intensity of shock wave [tex]I_{rms}=200MW/m^{2}[/tex]

**Attempt at an answer**

I have been able to do the first part of the question. I calculated the critical angle as [tex]\theta_{c}=arcsin(c_{urine}/c_{stone})=22°[/tex]

However, I don't know how to go from this to determining the energy delivered.

Thanks for any input.