# Which one of the following statements is NOT TRUE for a supersonic flow? (A) Over a gradual expansion, entropy remains constant (B) Over a sharp expansion corner, entropy can increase (C) Over a gradual compression, entropy can remain constant (D) Over a sharp compression corner, entropy increases

## Question ID - 156005 :- Which one of the following statements is NOT TRUE for a supersonic flow? (A) Over a gradual expansion, entropy remains constant (B) Over a sharp expansion corner, entropy can increase (C) Over a gradual compression, entropy can remain constant (D) Over a sharp compression corner, entropy increases

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(B) Over a sharp expansion corner, entropy can increase

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Consider a compressible flow where an elemental volume of the fluid is $\delta \vartheta,$ moving with velocity $\vec{V}$. Which one of the following expressions is TRUE?
(A) $\nabla \cdot \vec{V}=\frac{1}{\delta \vartheta} \frac{D \delta \vartheta}{D t}$
(B) $\nabla \cdot(\nabla \times \vec{V})=\frac{1}{\delta \vartheta} \frac{D \delta \vartheta}{D t}$
(C) $\nabla \cdot \frac{D \vec{V}}{D t}=\frac{1}{\delta \vartheta} \frac{D \delta \vartheta}{D t}$
(D) $\vec{V} \cdot(\nabla \times \vec{V})=\frac{1}{\delta \vartheta} \frac{D \delta \vartheta}{D t}$ 