Confused About Critical Angle and Echoes?

[Nubira20]

Homework Statement

One longitudinal US pulse was emitted inside a steel sheet that is 1cm wide at an angle of 15 o . Lubrication oil covers the backside of the steel sheet. You know that US velocity in steel is 6.2km/s and 4.1km/s for longitudinal and sheer waves, and 1.3km/s in oil. what is the (lateral) distance (on the sheet surface) between the source pulse and the longitudinal echo?

Relevant Equations

Snell's law

I calculated the first critical angle and found the incident angle here to be greater than it thus there no echoes because the beam didn't refract , but i asked a friend and he told me no and that he calculated a number .. any help ?

 

[berkeman]

Welcome to the PF.

Can you show your detailed calculations please? That will make it easier for us to help you. Thanks.

 

[haruspex]

Not sure I understand the set-up. Please post a diagram.