In supersonic flow passing through an oblique shock wave, changes behind the shock are:

• A. Static pressure increases; density increases; speed of sound increases
• B. Static pressure increases; density decreases; speed of sound increases
• C. Static pressure decreases; density increases; speed of sound increases
• D. Static pressure decreases; density decreases; speed of sound decreases

Answer: (A)

When a supersonic flow encounters an oblique shock, the flow is deflected and compressed. Across the shock, the gas is pushed together, so the static pressure rises. The compression also makes the density higher. Temperature increases as a consequence of the compression, and since the speed of sound a = sqrt(gamma R T), the increase in temperature means the speed of sound rises behind the shock. So the region behind the oblique shock has higher static pressure, higher density, and a higher speed of sound than before the shock. That matches the described changes.