能量方程中体积内动能和内能的总和是

1. A

   $\int_\tau \rho\frac{v^2}{2}\,d\tau$

2. B

   $\int_\tau \rho\left(U+\frac{v^2}{2}\right)d\tau$

   正确
3. C

   $\int_\tau \rho U\,d\tau$

4. D

   $\int_\tau \left(U+\frac{v^2}{2}\right)d\tau$