# Homework Help: Determining energy delivered from critical angle

1. Jan 18, 2013

### enc08

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.

$$\rho_{urine} = 1000kg/m^{3}, c_{urine} = 1000m/s, \rho_{stone} = 2000kg/m^{3}, c_{stone} = 4000m/s$$
Diameter of kidney stone $$d = 10mm$$
RMS intensity of shock wave $$I_{rms}=200MW/m^{2}$$

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