I'm not sure how to approach this problem. The teacher wants volumetric flow rate (in cm).

Question

A commonly used rule of thumb is that average velocity in a pipe should be about 1 m/s or less for "thin"(viscosity about water). If a pipe needs to deliver 6,000 m^3 of water a day, what diameter is required to satisfy the 1 m/s rule

Answer 1

if the diameter is d meters, the cross-section of the pipe has area pi/4 d^2 m^2

In one second, at 1 m/s, then, pi/4 d^2 m^3/s of water will flow through the pipe

now just plug in the numbers:

6000m^3/day * 1day/86400s = pi/4 d^2 m^3/s
d = 1/3 √(5/2pi) = 0.297m