The Equation of Continuity states the mass flow rate has the same value at every position along a tube that has a single entry and a single exit point for fluid flow.
Basically it boils down to the idea that the fluid doesn't disappear or appear from nowhere. If 2.0kg of fluid flows past a point in a tube in a time of 1.0s, then 2.0kg of fluid flows past another point in that tube in 1.0s as well. If the tube is getting larger or smaller, the velocity adjusts to keep the mass flow rate the same.
At Location One, fluid with a density of 1.01×103kg/m3 is flowing at speed of 3.56m/s through a circular pipe which has a radius of 7.900×10-2m. As the fluid flows along the pipe, the pipe gets larger. At Location Two the pipe has a radius of 1.888×10-1m (it is still circular in nature).
a) What is the cross-sectional area of the pipe at Location One?
b) What is the speed of the fluid at Location Two?