Question

Which of the following statement(s) is/are true across an oblique shock (in adiabatic conditions) over a wedge shown below? 

• A. Total pressure decreases
• B. Mach number based on velocity tangential to the shock decreases
• C. Total temperature remains constant
• D. Mach number based on velocity tangential to the shock remains the same and that based on velocity normal to the shock decreases

Hint:

Across an oblique shock: total pressure decreases, total temperature stays constant, tangential velocity stays unchanged while normal Mach number decreases.

Answer 1

The Correct Option is A, B, C

Step 1: Total pressure change across an oblique shock.
Across any adiabatic shock (normal or oblique), entropy increases, causing a loss of total pressure. Hence, total pressure always decreases. This makes option (A) correct.

Step 2: Tangential velocity behaviour.
Across an oblique shock, the tangential component of velocity remains unchanged. Since Mach number is proportional to velocity, the tangential Mach number does not decrease — it stays constant. Therefore, option (B) is incorrect and (D) is partially correct only for the normal component. However, since (D) claims both behaviors together incorrectly, it is eliminated.

Step 3: Total temperature.
For adiabatic flow with no external heat addition, total temperature remains constant across a shock. Thus option (C) is correct.

Final Answer: A, B, C