Assuming that there is no transformation of mass to energy or vice versa, it is possible to write a continuity equation for mass.

(a) If we use the continuity equation for charge as our model, what quantities correspond to J and ρν?

(b) Given a cube 1 cm on a side, experimental data show that the rates at which mass is leaving each of the six faces are 10.25, −9.85, 1.75, −2.00, −4.05, and 4.45 mg/s. If we assume that the cube is an incremental volume element, determine an approximate value for the time rate of change of density at its center.