1.

If \(\vec{f}\) is the body force of an infinitesimally small element (volume dx dy dz and density ρ) moving along with the flow (velocity \(\vec{V}\)), Which term is the work done by the body force?(a) \(\vec{f}.\vec{V}\)dx dy dz(b) \(\rho\vec{f}.\vec{V}\)(c) \(\rho\vec{f}.\vec{V}\)dx dy dz(d) \(\rho\vec{f}\)dx dy dzThe question was posed to me in a job interview.I want to ask this question from Energy Equation in section Governing Equations of Fluid Dynamics of Computational Fluid Dynamics

Answer»

Correct option is (c) \(\rho\vec{f}.\vec{V}\)dx DY dz

To elaborate: MASS = density×volume

mass = ρdx dy dz

rate of WORK done = FORCE×velocity

rate of work done = \(\rho\vec{f}.\vec{V}\)dx dy dz

\(\rho\vec{f}.\vec{V}\)dx dy dz is the work done by the body force.



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