- #1

- 115

- 1

**Problem:**

Material scientists have discovered a new fluid property called "radost" that is carried along with a fluid as it moves from one place to the next (just like a fluid's mass or momentum). Let ##r(x,y,z,t)## be the amount of radost/unit mass in a fluid. Let ##\rho(x,y,z,t)## be the mass density of the fluid. Let ##\vec{v}(x,y,z,t)## be the velocity vector of the fluid. Use the divergence theorem to derive a conservation law for radost.

**Attempt at a Solution:**

We did an example like this in class, but for conserving mass, so it was a little different. What we ended up with was the following expression [tex]\frac{\partial \rho}{\partial t}+\nabla \cdot (\rho \vec{v})=0[/tex]

We started by writing, [tex]dM=\rho dV[/tex] Thus, [tex]M=\int_V \rho dV[/tex] Then we applied the divergence theorem and that was basically it.

I'm just kind of confused how to start this one.