In a draining experiment, the depth of water above a small exit hole decreases from 0.40m to 0.10m. Neglecting viscosity, which statement best describes how the instantaneous mass flow rate m˙ through the hole changes over this interval?
a) m˙ becomes one–quarter its original value because exit speed is directly proportional to depth.
b) m˙ doubles because the pressure difference between the surface and the hole increases as the tank empties.
c) m˙ becomes one–half its original value because exit speed depends on the square root of depth.
d) m˙ remains constant because the density of the fluid does not change.