Question

Shock waves can occur both in subsonic and supersonic medium since the concerning equations are not concerned with whether M > 1 or M < 1.

(a) False

(b) True

This question was posed to me during a job interview.

My question is based upon Flow Compressible in division Normal Shock Waves of Aerodynamics

Answer 1

Right choice is (a) False

The explanation: Equations of mass, momentum, energy are valid in both super and subsonic mediums and hence shock wave can occur in both mediums. But, thermodynamics delete the possibility of shockwaves occurring in subsonic medium. Entropy change is negative if the upstream medium is subsonic and hence no shock waves occur in subsonic medium, else second law is violated.