Let ( hat{u} ) be the specific internal energy of a system moving along with the flow with a velocity ( vec{V} ). What is the time rate of change of the total energy of the system per unit mass?

• A. ( hat{u}+ frac{1}{2} vec{V}. vec{V} )
• B. ( frac{D}{Dt}( hat{u}+ frac{1}{2} vec{V}. vec{V}) )
• C. ( frac{ partial}{ partial t}( hat{u}+ frac{1}{2} vec{V}. vec{V}) )
• D. ( frac{D}{Dt}( hat{u}+ vec{V}. vec{V}) )